Momentum and force Flashcards
What is the equation for momentum?
momentum (kg m/s) = mass (kg) x velocity (m/s)
p = mv
What is the unit for momentum?
kg m/s
Name 3 car safety features, why they are needed, and what they do
- seat belts
- crumple zones
- air bags
they are needed because a large mass or deceleration of a vehicle results in large forces exerted on passengers, which is dangerous
they reduce the force exerted on passengers by increasing the time over which the vehicle comes to rest
by increasing the time it takes, the force is reduced (F= (mv - mu) ÷ t)
What does the momentum of a moving object depend on?
its mass and velocity
What type of quantity is momentum?
vector
What is force and what is the equation for force to do with change in momentum?
Force (N) = change in momentum (kg m/s) ÷ time taken (s)
F = mv - mu ÷ t
can be rearranged:
F = m(v - u) ÷ t
m = mass
A car of mass 1450 kg, travelling at 18 m/s, is brought to rest in 1.2 s. Calculate the force exerted on the car.
m = 1450 kg, u = 18 m/s, v = 0 m/s, t = 1.2 s
F= m(v - u) ÷ t
F = 1450 kg (0 m/s - 18 m/s) ÷ 1.2 s
= -21 750 N
A golfer wants to hit a golf ball with as much force as possible. Explain how the golfer does this.
The change in speed of the club and ball needs to be as high as possible and the contact time needs to be as small as possible. Both of these make the force as large as possible.
Calculate the momentum of a 25 kg trolley moving at 6 m/s.
m = 25 kg, v = 6 m/s
p = mv
p = 25 × 6
= 150 kg m/s
Calculate the force a car experiences when braking from 16 m/s to 7 m/s over a time period of 0.8 s when the car’s mass is 1580 kg.
m = 1580 kg, v = 7 m/s, u = 16 m/s, t = 0.8 s
F = m(v - u) ÷ t
F = 1580 (7 - 16) ÷ 0.8
= -17 775 N
Explain how the size of the force exerted on passengers in a car crash can be reduced.
Use safety features such as seat belts and crumple zones to increase the time taken for the car to decelerate/change in momentum so the force needed decreases.
