# Physics GCSE 2 aqa

- Created by: Skye Galpeer-Shade
- Created on: 18-06-13 22:09

First 550 words of the document:

Physics

Momentum and Collisions

Momentum = mass x velocity (p = m x v)

Momentum (p) is a property of moving objects.

The greater the mass of an object the greater its velocity and the more momentum the object has

Momentum has both size and direction (a vector)

Momentum for = momentum after (the conservation of momentum)

E.g. (COLLISIONS) Two skaters approach each other they collide and then move off together, at what

velocity do they move off together after the collision? (Skater 1 weighs 80kg and is moving at 2m/s to the

right and skater 2 weighs 60kg and is moving at 1.5m/s to the left)

o Choose which direction is positive. In this case positive means to the right.

o To calculate the momentum you times the velocity (so remember which way is positive) at which they

are going with their weight:

80 x 2 (the 2m/s being positive because skater 1 is moving to the right) = 160

60 x -1.5 (the 1.5m/s is negative because skater 2 is moving to the left) = -90

o Then you need to work out the total momentum before the collision, so:

160 90 = 70kg m/s

o Total momentum after the collision = total momentum before the collision

You need to work out the velocity to answer the question (v = p / m )

So p = 70 and m = 140 (80 + 60) so 70/ 140 = 0.5

The velocity and the answer to the question is 0.5 m/s to the right (because it's a positive

number)

E.g. (EXPLOSIONS) A gun fires a bullet at 150 m/s to the right. The gun weighs 1kg and the bullet weighs

0.01kg. We know it moves backwards to the left but at what speed does the gun move backwards?

o Choose which direction is positive in this case to the right

o The momentum before an explosion is 0 so total momentum before firing = 0kgm/s

o Total momentum after firing =

Momentum of bullet (0.01 x 150) + momentum of gun (1 x v) = 1.5 + v

o Because of the conservation of momentum the total momentum after must equal zero

So 1.5 + v = 0 = v = -1.5m/s so the gun moves backwards at 1.5m/s

The answer is 1.5m/s

Car Design and safety

Forces and change in momentum

Forces acting on an object changes their momentum

Larger force = faster change in momentum/ so greater acceleration (and vice versa)

So if someone's momentum changes very quickly in a car crash, the forces on the body will be very large and

more likely to cause injury

Cars are designed so that features in them will slow people down over a longer time slower change in

momentum = less force acting on the person

Cars are designed to convert kinetic energy safely in a crash

If a car crashes it will slow down very quickly this means that a lot of kinetic energy is converted into other

forms of energy in a short amount of time this can be dangerous

In a crash there will be a big change in momentum in a short time this creates a large force on the people

inside the car

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