Momentum
Contents
Key Stage 4 Higher
Meaning
Momentum is a vector quantity and the product of mass and velocity of an object.
About Momentum
- Momentum is a vector so it has magnitude and direction.
- The SI Units of momentum are kilogram metres per second (kgm/s).
- Momentum is conserved which means the total momentum before an interaction is the same as the total momentum after the interaction, see Conservation of Momentum.
- Forces cause a change in momentum. The quicker the change in momentum the greater the force applied to an object.
Equation
Momentum = Mass x Velocity
\(p = mv\)
Where
\(p\) = Momentum of the object.
\(m\) = Inertial Mass of the object.
\(v\) = Velocity of the object.
Example Calculations
Finding Momentum from Mass and Velocity
| A 21g bullet travels at a velocity of 600m/s. Calculate the momentum of the bullet correct to two significant figures. | A 7.6 tonne lorry travels at a velocity of 30m/s. Calculate the momentum of the bullet correct to two significant figures. |
| 1. State the known quantities
m = 21g = 0.021kg v = 610m/s |
1. State the known quantities
m = 7.6 tonnes = 7600kg v = 32m/s |
| 2. Substitute the numbers into the equation and solve.
\(p = mv\) \(p = 0.021 \times 610\) \(p = 12.81kgm/s\) \(p \approx 13kgm/s\) |
2. Substitute the numbers into the equation and solve.
\(p = mv\) \(p = 7600 \times 32\) \(p = 243200kgm/s\) \(p \approx 240000kgm/s\) |
Finding Velocity from Mass and Momentum
| Question | Question |
| 1. State the known quantities | 1. State the known quantities |
| 2. Substitute the numbers and evaluate. | 2. Substitute the numbers and evaluate. |
| 3. Rearrange the equation and solve. | 3. Rearrange the equation and solve. |
Finding Mass from Velocity and Momentum
| Question | Question |
| 1. State the known quantities | 1. State the known quantities |
| 2. Substitute the numbers and evaluate. | 2. Substitute the numbers and evaluate. |
| 3. Rearrange the equation and solve. | 3. Rearrange the equation and solve. |