Physics GCSE 2 aqa

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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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Cars are designed to convert this kinetic energy safely ­ they increase the time over which momentum
change happens ­ this lessens the force on the passenger
o E.g.…read more

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Only electrons can be transferred!
Opposites attract and likes repel
Charges can move easily through conductors (like metals)
Safety measures - higher tier only
The chance of receiving an electric shock can be reduced if:
An object that might become charged is connected to the Earth by an earth wire, so any charge
immediately flows down the earth wire.
In a factory, machinery operators stand on insulating mats or wear shoes with insulating soles. This
stops any charge flowing through them to the Earth.…read more

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