Answer Key for How
Things Work The
Physics of Everyday
Life, 6e Louis
Bloomfield (All
Chapters)
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, E.23 Zero net force.
Exercises – Chapter 1 E.24 The two push equally hard on one another (but in
opposite directions).
E.25 The astronaut exerts an upward force of 850 N on the
E.1 The dolphin’s inertia carries it upward, even though its earth.
weight makes it accelerate downward and gradually stop
rising. E.26 The car pushes you to the right with a force of 50 N.
E.2 There is no force keeping you moving forward. E.27 Both forces have exactly the same magnitude.
E.3 Your feet accelerate upward rapidly when they hit the E.28 The upward acceleration needed to stop the falling
ground and the snow continues downward, leaving your person is enough to injure them severely, whether the
feet behind. ground or a superhero exerts that force.
E.4 As the toothbrush stops suddenly, the water’s inertia E.29 The wall exerts a support force to accelerate you
keeps it going and it flies off the toothbrush. backward.
E.5 Any collision in which the car accelerates forward, such E.30 You do positive work when you pull the kite in.
as when the car is hit from behind by a faster moving
car. E.31 A person does more work. Movements that appear large
compared to the ant’s height still involve small distances
E.6 Nothing pushes on the driver, so the driver's inertia and little work.
causes the driver to coast forward and collide with the
steering wheel. E.32 Yes, you are doing work whenever you push on the
bread and it moves in the direction of that push.
E.7 As it turns left, the car accelerates left. The loose objects
remain behind and end up on the right side of the E.33 Yes, it pushed the wall inward and the wall dented
dashboard. inward.
E.8 Your direction of travel changes all the time and a E.34 In both cases, you do work on the saw: when you push it
change in direction involves an acceleration away from you as it moves away from you and as you
pull it toward you as it moves toward you.
E.9 Backward, in the direction opposite your forward
velocity. E.35 As it rolls on the surface, it always accelerates downhill.
E.10 The beans' inertias keep them from moving out of the E.36 The steeper the roof, the larger the downhill force on the
way. snow and debris and the more likely they are to slide off
the roof.
E.11 The anvil’s large mass slows its acceleration, so the hot
metal is squeezed between the moving hammer and the E.37 Its greatest acceleration is at the steepest point; its
stationary anvil. greatest speed is at the bottom of the slide.
E.12 The sprinter must overcome inertia and accelerate during E.38 The downhill force pushes you in the direction opposite
the first 100 m. During the second 100 m, the sprinter your motion and do negative work on you.
must simply maintain full speed. E.39 The kinetic energy becomes gravitational potential
E.13 The pad’s inertia tends to keep it in place. If you pull the energy.
paper away too quickly, the pad won’t be able to
Problems – Chapter 1
accelerate with the paper.
E.14 The ball's speed increases steadily, so there is no second
during which its speed increases most.
P.1 3200 N.
E.15 Regardless of their horizontal components of velocity, all
objects fall at the same rate. The ball and bullet descend P.2 It will take 6.15 seconds to reach 88.5 km/h.
together. P.3 11.13 m/s.
E.16 The acorn's average velocity during this second is less P.4 The rock will fall 16.7 meters during those 3 seconds.
than 9.8 m/s.
P.5 Your Mars weight would be about 38% of your earth
E.17 The forward component of his velocity remains constant weight.
as he falls, and he follows an arc that carries him forward
over the rocks. P.6 The basketball player's initial upward velocity is 3.1 m/s.
E.18 He should kick the ball straight up. P.7 About 0.64 s (0.32 s on the way up and 0.32 s on the way
down).
E.19 In the absence of air effects, a ball hit at 45° above
horizontal will travel farthest. A ball hit higher or lower P.8 The sprinter's acceleration is 10 m/s2
won’t travel as far.
P.9 48 N.
E.20 She experiences zero net force.
P.10 The 60-kg person weighs about 588 newtons.
E.21 Its magnitude must equal the suitcase’s weight.
P.11 About 0.20 s.
E.22 All three cars experience zero net force.
1
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, P.12 You will rise to a height of 0.20 meters. E.12 The closer the wire is to the axis of pliers' axis of
rotation, the less effective any force from the wire is at
P.13 4800 N producing a torque on the pliers and stopping its rotation.
P.14 The boxcar will have to accelerate for 70 seconds to E.13 The weights of your chest and your feet exert torques in
reach cruising speed. opposite directions about your knees. They partially
P.15 9800 N. balance one another.
P.16 It takes 9.8 million joules of work to raise a 20,000-kg E.14 The longer the pole is, the greater its rotational mass and
block 50 meters upward. the more torque that is required to start it rotating
significantly.
P.17 14,700,000 J.
E.15 It reduces the car’s rotational mass so that the car can
P.18 1000 kg of water releases 1.96 million joules of undergo rapid angular accelerations and change
gravitational potential energy in descending 200 meters. directions quickly.
P.19 12.5 J. E.16 A modest force exerted far from the pivot produces an
P.20 You have done 400 joules of work on the wedge. enormous force close to the pivot. Although the opener's
handle must travel a long distance, it produces the huge
P.21 8000 N. force on the bottle cap that's required to pull that cap off
the bottle.
P.22 You have done 30,000 joules of work.
E.17 By pushing far from the pivot, you exert more torque on
the lid.
Exercises – Chapter 2 E.18 The farther out the limb that your weight is exerted on
the branch, the larger the torque you produce on the limb
E.1 The angle by which the front, center seat would have to and the more likely it is to begin rotating.
be rotated, as viewed from above, to have each seat’s
E.19 Your small effort exerted on the crowbar far from its
orientation.
pivot produces a large force on the box, located near the
E.2 The propellers have rotational inertia (as measured by crowbar’s pivot.
their moments of inertia).
E.20 A modest upward force exerted on the handles far from
E.3 It would rotate about its center of mass, not its geometric the pivot can balance a large downward weight force
center. It would appear to wobble as it turned. exerted on the basket close to the pivot.
E.4 A boomerang or horseshoe's center of mass is in the air E.21 Skidding sideways does work against sliding friction,
between the two arms of the object. converting some of the skier’s kinetic energy into
thermal energy.
E.5 The wheel has rotational inertia, as measured by its
rotational mass, making it hard to start and stop E.22 The work that the horse does on the cart is wasted in
spinning. opposing friction. The work becomes thermal energy.
E.6 A force exerted directly toward or away from the axis of E.23 The pin’s surface turns with the crust and doesn’t slide
rotation produces zero torque about that axis of rotation. across it.
E.7 A force exerted at the hinges produces no torque about E.24 If the sprinter's foot slides backward, then friction from
them. the ground on the foot does negative work on the foot
and extracts energy from the sprinter. That energy
E.8 When you arm is pointing straight out in front of you, becomes thermal energy in the foot and ground.
any weight force exerted on your hand is at right angles
to the lever arm between your shoulder and hand and E.25 The nearer the frictional force is to the pivot, the less
produces a large torque about your shoulder. On the torque it produces to slow the yo-yo’s rotation.
other hand, when you arm is at your side, any weight Slipperiness reduces friction.
force exerted on your hand is directed away from your
E.26 The ground exerts a forward frictional force on the
shoulder and produces no torque about your shoulder.
bicycle wheel.
E.9 The farther the water is from the water wheel’s pivot, the
E.27 A static frictional force from the pavement pushes you
more torque its weight produces on the wheel.
forward.
E.10 The string pulls on the outside edge of the yo-yo's
E.28 The forward force you exert on the sled must balance the
spindle and at right angles to the lever arm between the
backward force that friction exerts on the sled.
yo-yo's rotational axis and the point at which the force
acts. As a result, it produces a torque on the yo-yo about E.29 Pressing the wheels more tightly against the pavement
its rotational axis and causes the yo-yo to undergo increases the maximum force that static friction can exert
angular acceleration. on the wheels.
E.11 Your force far from the hinges produces a large torque. E.30 While you are traveling straight at constant speed, you
To oppose this torque, the nut must exert a huge force are coasting and experience zero net force. It's only when
near the hinges. you try to accelerate horizontally that you need a
frictional force from the pavement and find yourself
sliding on ice instead.
2
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Things Work The
Physics of Everyday
Life, 6e Louis
Bloomfield (All
Chapters)
Downloaded by: tutorsection | Want to earn $1.236
Distribution of this document is illegal extra per year?
, E.23 Zero net force.
Exercises – Chapter 1 E.24 The two push equally hard on one another (but in
opposite directions).
E.25 The astronaut exerts an upward force of 850 N on the
E.1 The dolphin’s inertia carries it upward, even though its earth.
weight makes it accelerate downward and gradually stop
rising. E.26 The car pushes you to the right with a force of 50 N.
E.2 There is no force keeping you moving forward. E.27 Both forces have exactly the same magnitude.
E.3 Your feet accelerate upward rapidly when they hit the E.28 The upward acceleration needed to stop the falling
ground and the snow continues downward, leaving your person is enough to injure them severely, whether the
feet behind. ground or a superhero exerts that force.
E.4 As the toothbrush stops suddenly, the water’s inertia E.29 The wall exerts a support force to accelerate you
keeps it going and it flies off the toothbrush. backward.
E.5 Any collision in which the car accelerates forward, such E.30 You do positive work when you pull the kite in.
as when the car is hit from behind by a faster moving
car. E.31 A person does more work. Movements that appear large
compared to the ant’s height still involve small distances
E.6 Nothing pushes on the driver, so the driver's inertia and little work.
causes the driver to coast forward and collide with the
steering wheel. E.32 Yes, you are doing work whenever you push on the
bread and it moves in the direction of that push.
E.7 As it turns left, the car accelerates left. The loose objects
remain behind and end up on the right side of the E.33 Yes, it pushed the wall inward and the wall dented
dashboard. inward.
E.8 Your direction of travel changes all the time and a E.34 In both cases, you do work on the saw: when you push it
change in direction involves an acceleration away from you as it moves away from you and as you
pull it toward you as it moves toward you.
E.9 Backward, in the direction opposite your forward
velocity. E.35 As it rolls on the surface, it always accelerates downhill.
E.10 The beans' inertias keep them from moving out of the E.36 The steeper the roof, the larger the downhill force on the
way. snow and debris and the more likely they are to slide off
the roof.
E.11 The anvil’s large mass slows its acceleration, so the hot
metal is squeezed between the moving hammer and the E.37 Its greatest acceleration is at the steepest point; its
stationary anvil. greatest speed is at the bottom of the slide.
E.12 The sprinter must overcome inertia and accelerate during E.38 The downhill force pushes you in the direction opposite
the first 100 m. During the second 100 m, the sprinter your motion and do negative work on you.
must simply maintain full speed. E.39 The kinetic energy becomes gravitational potential
E.13 The pad’s inertia tends to keep it in place. If you pull the energy.
paper away too quickly, the pad won’t be able to
Problems – Chapter 1
accelerate with the paper.
E.14 The ball's speed increases steadily, so there is no second
during which its speed increases most.
P.1 3200 N.
E.15 Regardless of their horizontal components of velocity, all
objects fall at the same rate. The ball and bullet descend P.2 It will take 6.15 seconds to reach 88.5 km/h.
together. P.3 11.13 m/s.
E.16 The acorn's average velocity during this second is less P.4 The rock will fall 16.7 meters during those 3 seconds.
than 9.8 m/s.
P.5 Your Mars weight would be about 38% of your earth
E.17 The forward component of his velocity remains constant weight.
as he falls, and he follows an arc that carries him forward
over the rocks. P.6 The basketball player's initial upward velocity is 3.1 m/s.
E.18 He should kick the ball straight up. P.7 About 0.64 s (0.32 s on the way up and 0.32 s on the way
down).
E.19 In the absence of air effects, a ball hit at 45° above
horizontal will travel farthest. A ball hit higher or lower P.8 The sprinter's acceleration is 10 m/s2
won’t travel as far.
P.9 48 N.
E.20 She experiences zero net force.
P.10 The 60-kg person weighs about 588 newtons.
E.21 Its magnitude must equal the suitcase’s weight.
P.11 About 0.20 s.
E.22 All three cars experience zero net force.
1
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Distribution of this document is illegal extra per year?
, P.12 You will rise to a height of 0.20 meters. E.12 The closer the wire is to the axis of pliers' axis of
rotation, the less effective any force from the wire is at
P.13 4800 N producing a torque on the pliers and stopping its rotation.
P.14 The boxcar will have to accelerate for 70 seconds to E.13 The weights of your chest and your feet exert torques in
reach cruising speed. opposite directions about your knees. They partially
P.15 9800 N. balance one another.
P.16 It takes 9.8 million joules of work to raise a 20,000-kg E.14 The longer the pole is, the greater its rotational mass and
block 50 meters upward. the more torque that is required to start it rotating
significantly.
P.17 14,700,000 J.
E.15 It reduces the car’s rotational mass so that the car can
P.18 1000 kg of water releases 1.96 million joules of undergo rapid angular accelerations and change
gravitational potential energy in descending 200 meters. directions quickly.
P.19 12.5 J. E.16 A modest force exerted far from the pivot produces an
P.20 You have done 400 joules of work on the wedge. enormous force close to the pivot. Although the opener's
handle must travel a long distance, it produces the huge
P.21 8000 N. force on the bottle cap that's required to pull that cap off
the bottle.
P.22 You have done 30,000 joules of work.
E.17 By pushing far from the pivot, you exert more torque on
the lid.
Exercises – Chapter 2 E.18 The farther out the limb that your weight is exerted on
the branch, the larger the torque you produce on the limb
E.1 The angle by which the front, center seat would have to and the more likely it is to begin rotating.
be rotated, as viewed from above, to have each seat’s
E.19 Your small effort exerted on the crowbar far from its
orientation.
pivot produces a large force on the box, located near the
E.2 The propellers have rotational inertia (as measured by crowbar’s pivot.
their moments of inertia).
E.20 A modest upward force exerted on the handles far from
E.3 It would rotate about its center of mass, not its geometric the pivot can balance a large downward weight force
center. It would appear to wobble as it turned. exerted on the basket close to the pivot.
E.4 A boomerang or horseshoe's center of mass is in the air E.21 Skidding sideways does work against sliding friction,
between the two arms of the object. converting some of the skier’s kinetic energy into
thermal energy.
E.5 The wheel has rotational inertia, as measured by its
rotational mass, making it hard to start and stop E.22 The work that the horse does on the cart is wasted in
spinning. opposing friction. The work becomes thermal energy.
E.6 A force exerted directly toward or away from the axis of E.23 The pin’s surface turns with the crust and doesn’t slide
rotation produces zero torque about that axis of rotation. across it.
E.7 A force exerted at the hinges produces no torque about E.24 If the sprinter's foot slides backward, then friction from
them. the ground on the foot does negative work on the foot
and extracts energy from the sprinter. That energy
E.8 When you arm is pointing straight out in front of you, becomes thermal energy in the foot and ground.
any weight force exerted on your hand is at right angles
to the lever arm between your shoulder and hand and E.25 The nearer the frictional force is to the pivot, the less
produces a large torque about your shoulder. On the torque it produces to slow the yo-yo’s rotation.
other hand, when you arm is at your side, any weight Slipperiness reduces friction.
force exerted on your hand is directed away from your
E.26 The ground exerts a forward frictional force on the
shoulder and produces no torque about your shoulder.
bicycle wheel.
E.9 The farther the water is from the water wheel’s pivot, the
E.27 A static frictional force from the pavement pushes you
more torque its weight produces on the wheel.
forward.
E.10 The string pulls on the outside edge of the yo-yo's
E.28 The forward force you exert on the sled must balance the
spindle and at right angles to the lever arm between the
backward force that friction exerts on the sled.
yo-yo's rotational axis and the point at which the force
acts. As a result, it produces a torque on the yo-yo about E.29 Pressing the wheels more tightly against the pavement
its rotational axis and causes the yo-yo to undergo increases the maximum force that static friction can exert
angular acceleration. on the wheels.
E.11 Your force far from the hinges produces a large torque. E.30 While you are traveling straight at constant speed, you
To oppose this torque, the nut must exert a huge force are coasting and experience zero net force. It's only when
near the hinges. you try to accelerate horizontally that you need a
frictional force from the pavement and find yourself
sliding on ice instead.
2
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