Summary Grade 12 IEB Physical Science: Momentum, Impulse, Work, Energy and Power

MOMENTUM, IMPULSE, WORK,
ENERGY AND POWER




@STUDYNOTESBYM

, C. MOMENTUM, IMPULSE, WORK, ENERGY AND POWER



1. LINEAR MOMENTUM (1D)

Linear momentum is the product of the mass and velocity of the object



p=mv
p: momentum measured in 𝑘𝑔. 𝑚. 𝑠 −1

m: mass measured in 𝑘𝑔

v: velocity measured in 𝑚. 𝑠 −1



• Momentum is a vector quantity (has a magnitude and direction) and is in the same
direction as the velocity
e.g.) if velocity is acting right, momentum will also act right


CALCULATING LINEAR MOMENTUM:
Example: A 500kg car drives along a city street at 13.4m/s. What is the car’s momentum?
Let forward be positive
1. Assign a positive
𝑝 = 𝑚𝑣 direction
= (500)(13.4) 2. Use the formula to
= 6700𝑘𝑔. 𝑚. 𝑠 −1 𝑓𝑜𝑟𝑤𝑎𝑟𝑑 calculate the
magnitude of the
momentum
3. State a direction

, 2. NEWTON’S SECOND LAW EXPRESSED IN TERMS OF MOMENTUM
(THE CHANGE IN MOMENTUM - ∆𝑃 )

The net force acting on an object is equal to the rate of change of momentum




∆𝒑
𝑭𝒓𝒆𝒔 =
∆𝒕
When an object experiences a resultant force, it will accelerate. Because it
accelerates, the velocity changes therefore the momentum of the object will
change:

∆𝒑 = 𝒎(𝑽𝒇 − 𝑽𝒊)
Therefore:


𝒎(𝑽𝒇 − 𝑽𝒊)
𝑭𝒓𝒆𝒔 =
∆𝒕


Example:
A 500g ball, travelling at 14m/s, is kicked. The ball moves off in the opposite direction at a speed
of 18m/s. If the ball was in contact with the kicker’s foot for 0.05s, calculate the resultant force
exerted on the ball
∆𝑝
𝐹𝑟𝑒𝑠 =
∆𝑡


𝑚(𝑉𝑓 − 𝑉𝑖 )
=
∆𝑡
0,5(−18 − 14)
=
0,05
= −320
= 320𝑁 𝑖𝑛 𝑡ℎ𝑒 𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑘𝑖𝑐𝑘𝑒𝑟 ′ 𝑠 𝑓𝑜𝑜𝑡