Section 1: Momentum

Question 1

What determines how large a force you need to apply to alter a motion of an object?

Answer 1

1. How quickly you want to stop it
2. Its velocity
3. Its mass

Question 2

Equation for Momentum

Answer 2

momentum = mass x velocity

kgm/s kg m/s

Question 3

Factors affecting the thinking distance

Answer 3

• tiredness
• intoxication
• influence of drugs

Question 4

Factors affecting the braking distance

Answer 4

• wet/icy road surface

- condition of brakes + tyres

Question 5

Newton’s 1st law

Answer 5

An object stays stationary unless acted on by an external force

Question 6

Newton’s 2nd law

Answer 6

F = ma
(acceleration = rate of change of velocity)

Question 7

Newton’s 3rd law

Answer 7

For every action there is an equal and opposite reaction

Question 8

What equation links force, momentum and time?

Answer 8

F = △P/△t

F = ma
a = (v - u)/ t

therefore: F = m (v - u)/t
F = (mv - mu)/ t

Question 9

How to calculate the change in momentum?

Answer 9

△P = mv-mu

final mom - initial mom

Question 10

For a given momentum change, how can the force be reduced?

Answer 10

Increase the time it takes for the momentum of an object to change to reduce the force it experience.

F =△P
time take

Question 11

Why does the surface of a playground have a rubbery surface?

Answer 11

Rubbery surfaces can compress, thus increasing the time taken to change momentum of a child if they fall

Question 12

Why do cars have:

a) an airbag?
b) a seatbelt
c) crumple zone?

Answer 12

• airbags inflate to increase the impact time, reducing the rate of change of momentum of the head as well as spreading the force over a large area
• seat belts are designed to stretch, lowering the rate of change of momentum
• crumple zones increase the impact time

Question 13

Elastic collision

Answer 13

Momentum is conserved and no kinetic energy is lost

particles collisions

Question 14

Conservation of momentum

Answer 14

The total momentum before a collision is the same as after

Question 15

Inelastic collision

Answer 15

Momentum is conserved but some kinetic energy is transferred

(usually everyday collisions)

Question 16

Work out the velocity of the recoil of the gun if:

• the gun has mass of 2 kg
• it fires a bullet of 10 g that travels 260 m/s

Answer 16

*explosion type question
momentum before = momentum after
momentum of gun = 0

0. 01 x 260 = 2.6
1. 6 / 1.99 = 1.3 m/s

Question 17

What’s the equation linking kinetic energy, mass and speed?

Answer 17

KE = 1/2 x mv2

Question 18

How do jets and rockets fly?

Answer 18

Jet + rocket engines burn fuel which produces high pressure exhaust gases which escape through the back, exerting a force.

The reaction force of the exhaust gas on the vehicle pushes it forward

Question 19

If 2 forces are a Newton’s 3rd law pair of forces they must

Answer 19

1. equal in size
2. oposite in direction
3. same type of force
4. acting on 2 objects

Question 20

action/ reaction force when Eskimo pushes box on ice

Answer 20

Eskimo pushes box forward, the box pushes back in equal force and opposite direction

Question 21

Why do weapons have a recoil?

Answer 21

Due to Newton’s 3rd law, when a bullet is fired from the gun the bullet also exerts an equal and opposite force on the gun, causing it to move back. This shows momentum is a vector quantity

Question 22

What is momentum

Answer 22

Momentum is a quantity possessed by masses in motions

It’s a measure of how difficult it is to stop something from moving