1.23 use the relationship between force, change in momentum and time taken

force (N) = change in momentum (kg m/s) / time taken (s)

1.22 use the conservation of momentum to calculate the mass, velocity or momentum of objects

Remember:
Momentum before = momentum after
This means all the momentum has to have gone somewhere.
e.g.
A 1kg gun fires a bullet at 0.01kg bullet at 150m/s. 
Find the velocity of the gun backwards!

1. Total momentum before firing = 0 kg m/s
2. Total momentum after firing = momentum of bullet + momentum of gun = (0.01 x 150) + (1 x v)
3. So total momentum after firing = 1.5 + v
4. Plug that into the momentum before = momentum after > 1.5 + v = 0
5. Rearrange > v = -1.5 m/s

NB - from the beginning identify the unknown and put it into the formula e.g v

Overall, use the two formulas momentum before = momentum after and momentum = mass x velocity

1.21 use the idea of momentum to explain safety features

In an exam this would usually ask you something about a car.
Remember force = change in momentum / time taken. This means that if your momentum takes longer to change then you will experience less of a force.
Car manufacturers etc. use this to reduce the impact of crashes with seatbelts etc.

1.20 know and use the relationship between momentum, mass and velocity: momentum = mass × velocity p = m × v

momentum = mass × velocity

Always use kg for the mass and m/s for the velocity:

momentum (kg m/s) = mass (kg) x velocity (m/s)

1.1 Use the following units: kilogram metre/second (kg m/s).

Momentum

kg m/s is the unit of momentum.