Physics 121 Final Exam Questions
and Answers All Correct
A quarterback throws a football from shoulder level to a receiver downfield, who catches
it at shoulder level. At what point in the motion of the ball is its speed a minimum?
(Assume air resistance is negligible.)
a. Just after leaving the quarterback's hand.
b. Just before the receiver catches it.
c. At the peak of its motion.
d. The speed is constant throughout its motion. - Answer-The correct answer is (c). The
speed is a minimum when the y-component of the velocity is at a minimum, because the
x-component of the velocity is constant. The y-component of the velocity is zero at the
peak.
A man standing on the rear platform of a caboose of a train which is traveling due north
at a speed of 60 miles/hour relative to the ground. While there he throws a baseball due
south at a speed of 60 miles/hour, relative to the train. What will happen to the ball?
(Assume the ball is not influenced by any wind currents.)
a. The ball will travel southward from the point where it is thrown.
b. The ball will travel northward from the point where it is thrown.
c. The ball will fall straight down to the ground.
d. It will depend on the mass and size of the ball. - Answer-The correct answer is (c).
The horizontal velocities will cancel each other, leaving the ball to just fall vertically to
the ground.
Three balls are simultaneously shot from the top of a tower. One is fired at an angle of
10 degrees above the horizontal, the second is fired straight horizontally, and the third is
fired at an angle of 10 degrees below the horizontal. The three balls all have different
speeds. Which of the balls strikes the ground first?
a. The ball fired at 10 degrees above the horizontal.
b. The ball fired horizontally.
c. The ball fired at 10 degrees below the horizontal.
d. They all strike the ground at the same time.
e. You cannot tell from the given information. - Answer-The correct answer is (c). The
horizontal velocity doesn't matter, because the motions are independent. The key thing
is that the first ball has some upward velocity, the second has zero upward velocity and
the third has some downward velocity. Something in free-fall that starts with some
,downward velocity always hits the ground before something that is going upward or just
dropped.
(fig4)
A car is moving in a circular path as shown in the figure. The radius of the circle is R
and the speed of the car is v. The four positions marked J, K, L, and M correspond to
the four spots marked with Xs on the diagram
If the car is moving at a constant speed around the circle, which arrow below best
shows the acceleration of the car when it is at location M, as shown? - Answer-The
correct answer is (G). An object moving with constant speed in a circle has centripetal
acceleration, which points straight to the center of the circle.
(fig4)
A car is moving in a circular path as shown in the figure. The radius of the circle is R
and the speed of the car is v. The four positions marked J, K, L, and M correspond to
the four spots marked with Xs on the diagram
If the driver is applying the brakes as the car goes around the circle, so that the car is
slowing down, which of the arrows in question 5 best illustrates the direction of the
acceleration of the car when it is at position M? - Answer-The correct answer is (F).
There is still the centripetal (or radial) component of the acceleration, but there is also a
tangential part. Since the car is slowing down, the tangential part must be opposite to
the velocity, or downward in the figure. So (F) represents the vector sum of those two
accelerations.
(fig4)
A car is moving in a circular path as shown in the figure. The radius of the circle is R
and the speed of the car is v. The four positions marked J, K, L, and M correspond to
the four spots marked with Xs on the diagram
If the car were going twice as fast and the radius of the path was twice as large, the
acceleration would change by a factor of
a. One-fourth.
b. One-half.
c. One (it would remain the same.)
d. Two.
e. Four. - Answer-The correct answer is (d). The acceleration is v2/r. Both v and r are
increased by a factor of 2, so the acceleration is (2)2/2 = 4/2 = 2 times larger.
(fig4)
A car is moving in a circular path as shown in the figure. The radius of the circle is R
and the speed of the car is v. The four positions marked J, K, L, and M correspond to
the four spots marked with Xs on the diagram
,Under what conditions could the acceleration vector be vector B as shown in problem
5?
a. When the car is at position K and slowing down.
b. When the car is at position J and speeding up.
c. When the car is at position L and slowing down.
d. When the car is at position M and speeding up. - Answer-The correct answer is (a).
At K the radial acceleration is to the right and a slowing down car would create an
upward tangential acceleration, making vector B possible. (b) is not possible because
both the radial and tangential components are in the wrong direction. (c) is not possible
because the tangential component would be wrong. (d) is not possible because the
radial component is backward.
A cannon shoots a cannonball with an initial speed v. It lands at the same height that it
started at, 100 m away. Where in its path will the acceleration and velocity vectors be
parallel?
a. Just at the peak of the motion.
b. Just before it lands.
c. Just after it is shot.
d. Both b and c.
e. Never - Answer-he correct answer is (e). The acceleration is straight down. The
velocity is never straight down, so (e) is the correct answer.
(fig5)
A cannon can shoot at two different angles, θ1 and θ2, that both have the same range,
i.e. the cannonball hits at the same location for both angles, as shown below. The
speed of the cannonball is the same for both angles.
The cannonball spends more time in the air when shot at angle
a. θ1
b. θ2
c. It spends the same amount of time with both θ 1 and θ 2. - Answer-The correct
answer is (b). Angle θ 2 has the largest y-component of velocity, so it spends the most
time in the air.
(fig5)
A cannon can shoot at two different angles, θ1 and θ2, that both have the same range,
i.e. the cannonball hits at the same location for both angles, as shown below. The
speed of the cannonball is the same for both angles.
The cannonball has the largest horizontal velocity when shot at angle
a. θ1
b. θ2
c. It is the same for both θ1 and θ2.
d. It depends on the circumstances. - Answer-The correct answer is (a). The largest x-
component of velocity occurs when shot at angle θ 1.
, (fig5)
A cannon can shoot at two different angles, θ1 and θ2, that both have the same range,
i.e. the cannonball hits at the same location for both angles, as shown below. The
speed of the cannonball is the same for both angles.
The cannonball has less than the maximum possible range when shot at both θ 1 and θ
2. Why is that?
a. The horizontal velocity is too low to allow it to go that far in the time it is in the air.
b. There is enough horizontal velocity, but there isn't enough time before it hits the
ground to let it reach the maximum range.
c. It could be either a or b, depending on the angle.
d. The acceleration in the horizontal direction is too large, slowing it down so that it can't
go far enough in the time it has.
e. The acceleration in the horizontal direction is too small, limiting the amount of time it
spends in the air. - Answer-The correct answer is (c). Answer (a) is the correct
explanation for angle θ 2 and answer (b) is the correct explanation for angle θ 1.
Answers (d) and (e) are wrong because there is no acceleration in the horizontal
direction.
A canoeist plans on paddling across two bodies of water. The first is the Mississippi
river and the other is a lake of equal width. In both cases he wants to land at a point
perpendicular to the shore, straight across the body of water. In which case will he take
longer to get across, assuming his paddling speed is the same in both cases?
a. Crossing the Mississippi.
b. Crossing the lake.
c. It will be the same in both cases. - Answer-The correct answer is (a). In order to land
at a place perpendicular to the shore on the Mississippi river he will have to paddle
upstream to compensate for the flow of the river. This means that he will have only the
perpendicular component of his velocity across the river, which is less than his full
paddling speed, therefore taking more time. On the lake he will have the entire paddling
speed to use to cross the lake. If the flow speed of the Mississippi were equal to his
paddling speed, he would take forever to cross the river, since he would have to paddle
straight upstream and would end up going nowhere!
**The weight of an object
a. is the quantity of matter that it contains.
b. refers to its inertia.
c. is the force of attraction between the object and the Earth.
d. is basically the same quantity as its mass, but expressed in different units. - Answer-
The correct answer is (c). The weight is a force and it represents the gravitational pull of
the Earth on the object.
**The force of kinetic friction is always directed opposite to
a. the force of gravity.
b. the normal force.
c. the direction of motion.
and Answers All Correct
A quarterback throws a football from shoulder level to a receiver downfield, who catches
it at shoulder level. At what point in the motion of the ball is its speed a minimum?
(Assume air resistance is negligible.)
a. Just after leaving the quarterback's hand.
b. Just before the receiver catches it.
c. At the peak of its motion.
d. The speed is constant throughout its motion. - Answer-The correct answer is (c). The
speed is a minimum when the y-component of the velocity is at a minimum, because the
x-component of the velocity is constant. The y-component of the velocity is zero at the
peak.
A man standing on the rear platform of a caboose of a train which is traveling due north
at a speed of 60 miles/hour relative to the ground. While there he throws a baseball due
south at a speed of 60 miles/hour, relative to the train. What will happen to the ball?
(Assume the ball is not influenced by any wind currents.)
a. The ball will travel southward from the point where it is thrown.
b. The ball will travel northward from the point where it is thrown.
c. The ball will fall straight down to the ground.
d. It will depend on the mass and size of the ball. - Answer-The correct answer is (c).
The horizontal velocities will cancel each other, leaving the ball to just fall vertically to
the ground.
Three balls are simultaneously shot from the top of a tower. One is fired at an angle of
10 degrees above the horizontal, the second is fired straight horizontally, and the third is
fired at an angle of 10 degrees below the horizontal. The three balls all have different
speeds. Which of the balls strikes the ground first?
a. The ball fired at 10 degrees above the horizontal.
b. The ball fired horizontally.
c. The ball fired at 10 degrees below the horizontal.
d. They all strike the ground at the same time.
e. You cannot tell from the given information. - Answer-The correct answer is (c). The
horizontal velocity doesn't matter, because the motions are independent. The key thing
is that the first ball has some upward velocity, the second has zero upward velocity and
the third has some downward velocity. Something in free-fall that starts with some
,downward velocity always hits the ground before something that is going upward or just
dropped.
(fig4)
A car is moving in a circular path as shown in the figure. The radius of the circle is R
and the speed of the car is v. The four positions marked J, K, L, and M correspond to
the four spots marked with Xs on the diagram
If the car is moving at a constant speed around the circle, which arrow below best
shows the acceleration of the car when it is at location M, as shown? - Answer-The
correct answer is (G). An object moving with constant speed in a circle has centripetal
acceleration, which points straight to the center of the circle.
(fig4)
A car is moving in a circular path as shown in the figure. The radius of the circle is R
and the speed of the car is v. The four positions marked J, K, L, and M correspond to
the four spots marked with Xs on the diagram
If the driver is applying the brakes as the car goes around the circle, so that the car is
slowing down, which of the arrows in question 5 best illustrates the direction of the
acceleration of the car when it is at position M? - Answer-The correct answer is (F).
There is still the centripetal (or radial) component of the acceleration, but there is also a
tangential part. Since the car is slowing down, the tangential part must be opposite to
the velocity, or downward in the figure. So (F) represents the vector sum of those two
accelerations.
(fig4)
A car is moving in a circular path as shown in the figure. The radius of the circle is R
and the speed of the car is v. The four positions marked J, K, L, and M correspond to
the four spots marked with Xs on the diagram
If the car were going twice as fast and the radius of the path was twice as large, the
acceleration would change by a factor of
a. One-fourth.
b. One-half.
c. One (it would remain the same.)
d. Two.
e. Four. - Answer-The correct answer is (d). The acceleration is v2/r. Both v and r are
increased by a factor of 2, so the acceleration is (2)2/2 = 4/2 = 2 times larger.
(fig4)
A car is moving in a circular path as shown in the figure. The radius of the circle is R
and the speed of the car is v. The four positions marked J, K, L, and M correspond to
the four spots marked with Xs on the diagram
,Under what conditions could the acceleration vector be vector B as shown in problem
5?
a. When the car is at position K and slowing down.
b. When the car is at position J and speeding up.
c. When the car is at position L and slowing down.
d. When the car is at position M and speeding up. - Answer-The correct answer is (a).
At K the radial acceleration is to the right and a slowing down car would create an
upward tangential acceleration, making vector B possible. (b) is not possible because
both the radial and tangential components are in the wrong direction. (c) is not possible
because the tangential component would be wrong. (d) is not possible because the
radial component is backward.
A cannon shoots a cannonball with an initial speed v. It lands at the same height that it
started at, 100 m away. Where in its path will the acceleration and velocity vectors be
parallel?
a. Just at the peak of the motion.
b. Just before it lands.
c. Just after it is shot.
d. Both b and c.
e. Never - Answer-he correct answer is (e). The acceleration is straight down. The
velocity is never straight down, so (e) is the correct answer.
(fig5)
A cannon can shoot at two different angles, θ1 and θ2, that both have the same range,
i.e. the cannonball hits at the same location for both angles, as shown below. The
speed of the cannonball is the same for both angles.
The cannonball spends more time in the air when shot at angle
a. θ1
b. θ2
c. It spends the same amount of time with both θ 1 and θ 2. - Answer-The correct
answer is (b). Angle θ 2 has the largest y-component of velocity, so it spends the most
time in the air.
(fig5)
A cannon can shoot at two different angles, θ1 and θ2, that both have the same range,
i.e. the cannonball hits at the same location for both angles, as shown below. The
speed of the cannonball is the same for both angles.
The cannonball has the largest horizontal velocity when shot at angle
a. θ1
b. θ2
c. It is the same for both θ1 and θ2.
d. It depends on the circumstances. - Answer-The correct answer is (a). The largest x-
component of velocity occurs when shot at angle θ 1.
, (fig5)
A cannon can shoot at two different angles, θ1 and θ2, that both have the same range,
i.e. the cannonball hits at the same location for both angles, as shown below. The
speed of the cannonball is the same for both angles.
The cannonball has less than the maximum possible range when shot at both θ 1 and θ
2. Why is that?
a. The horizontal velocity is too low to allow it to go that far in the time it is in the air.
b. There is enough horizontal velocity, but there isn't enough time before it hits the
ground to let it reach the maximum range.
c. It could be either a or b, depending on the angle.
d. The acceleration in the horizontal direction is too large, slowing it down so that it can't
go far enough in the time it has.
e. The acceleration in the horizontal direction is too small, limiting the amount of time it
spends in the air. - Answer-The correct answer is (c). Answer (a) is the correct
explanation for angle θ 2 and answer (b) is the correct explanation for angle θ 1.
Answers (d) and (e) are wrong because there is no acceleration in the horizontal
direction.
A canoeist plans on paddling across two bodies of water. The first is the Mississippi
river and the other is a lake of equal width. In both cases he wants to land at a point
perpendicular to the shore, straight across the body of water. In which case will he take
longer to get across, assuming his paddling speed is the same in both cases?
a. Crossing the Mississippi.
b. Crossing the lake.
c. It will be the same in both cases. - Answer-The correct answer is (a). In order to land
at a place perpendicular to the shore on the Mississippi river he will have to paddle
upstream to compensate for the flow of the river. This means that he will have only the
perpendicular component of his velocity across the river, which is less than his full
paddling speed, therefore taking more time. On the lake he will have the entire paddling
speed to use to cross the lake. If the flow speed of the Mississippi were equal to his
paddling speed, he would take forever to cross the river, since he would have to paddle
straight upstream and would end up going nowhere!
**The weight of an object
a. is the quantity of matter that it contains.
b. refers to its inertia.
c. is the force of attraction between the object and the Earth.
d. is basically the same quantity as its mass, but expressed in different units. - Answer-
The correct answer is (c). The weight is a force and it represents the gravitational pull of
the Earth on the object.
**The force of kinetic friction is always directed opposite to
a. the force of gravity.
b. the normal force.
c. the direction of motion.
