Starter quiz
- Which of the following is the product of the mass and velocity (mass × velocity) of an object?
- resultant force
- acceleration
- momentum ✓
- moment
- kinetic energy
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- Which of the following is the correct unit of momentum?
- kg m
- m/s
- kg m/s ✓
- kg m/s
- kg m/s
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- According to the principle of conservation of momentum, which of the following statements is correct?
- The momentum of an individual object in the system cannot increase.
- The momentum of an individual object in the system cannot decrease.
- The velocity of an individual object in the system cannot increase.
- The velocity of an individual object in the system cannot decrease.
- The total momentum of all objects in a closed system cannot change. ✓
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- Starting with the greatest momentum, sort the following objects into order of decreasing momentum.
- 1⇔a bus of mass 3000 kg travelling at 1 m/s
- 2⇔a car of mass 800 kg travelling at 2 m/s
- 3⇔a skater of mass 60 kg travelling at 8 m/s
- 4⇔a stationary train of mass 300 000 kg
- A bicycle and rider have a combined mass of 100 kg. Calculate their acceleration when a resultant force of 250 N acts on them.
- 0.40 m/s
- 2.5 m/s ✓
- 3.5 m/s
- 150 m/s
- 400 m/s
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- A van of mass 2000 kg accelerates in a straight line from 5.0 m/s to 8.0 m/s. Calculate the increase in momentum for the van. You do not need to give the unit.
- '6000' ✓
Exit quiz
- Match the following key terms to their definition.
- momentum⇔the product of the mass and velocity of an object, ✓
- initial velocity⇔the velocity of an object at the start of a phase of motion, ✓
- final velocity⇔the velocity of an object at the end of a phase of motion, ✓
- rate of change of momentum⇔the change in momentum per second, equal to the resultant force ✓
- A bus of mass 4000 kg accelerates from 2.0 m/s to 4.5 m/s. Calculate the change in momentum of the bus.
- 1 600 kg m/s
- 8 000 kg m/s
- 10 000 kg m/s ✓
- 18 000 kg m/s
- 26 000 kg m/s
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- A ball of mass 0.40 kg hits a wall at a velocity of 3.0 m/s. It bounces off in the opposite direction at 2.5 m/s. Calculate the change in momentum for the ball.
- –1.0 kg m/s
- –1.2 kg m/s
- –2.0 kg m/s
- –2.2 kg m/s ✓
- –3.0 kg m/s
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- Which of the following is equal to the rate of change of momentum of an object?
- acceleration
- increase in mass
- rate of change of velocity
- size of the resultant force acting on it ✓
- rate of increase of kinetic energy
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- A pickup truck of mass 2000 kg is travelling at 12 m/s. It slows to 4 m/s in a time of 5 s. Calculate the size of the force needed to do this.
- –1250 N
- –1600 N
- –3200 N ✓
- –4800 N
- –80 000 N
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- A ball with mass 0.30 kg and speed 5.0 m/s hits a wall and bounces back, at the same speed, in the opposite direction. The impact lasts for 0.10 s. Calculate the size of the force during the impact.
- '-30 N' ✓
Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- The momentum of an object is changed by a resultant force acting over a period of time.
- Force = rate of change of momentum, F = Δp ÷ t = (mv – mu) ÷ t
- The size of an impact force can be changed when the duration of the impact changes.
Common misconception
Pupils often confuse the terms force and momentum.
Make explicit the understanding that forces change the motion of an object, and that the motion of an object (that a force can change) can be described by its momentum.
Keywords
Momentum - is the product of the mass and velocity of an object, p = m v, it is a vector quantity
Initial velocity, u - is the velocity of an object at the start of a phase of motion, represented by u
Final velocity, v - is the velocity of an object at the end of a phase of motion, represented by v
Rate of change of momentum - is the change in momentum per second, this is equal to the resultant force acting on an object
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