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TOPIC 4 ­ momentum, energy, work and power

Stopping distance is the time it takes a car to stop and it depends on
two factors:
1. Thinking distance ­ distance travelled in between the driver
noticing the hazard and applying the brakes. Factors that
affects thinking distance are:
Greater speed…

Page 2

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your foot forward. The result is that you move forward but the floor
stays still.
Common experiment is to show change in friction with different

The greater the forces needed to pull the block, the higher the
The smaller the friction between block and surface, the smaller the…

Page 3

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Momentum of bullet = mass × velocity
= 0.03 kg × 1,000 m/s = 30 kg m/s
Rearrange the equation: velocity = momentum ÷ mass
Velocity of recoil on gun = 30 kg m/s ÷ 1.5 kg = 20 m/s

Car safety
In a car crash, the great forces caused…

Page 4

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Whenever work is done energy is transferred from one place to
another. Everyday examples include walking up the stairs or lifting
heavy objects.
Both energy and work are measured in joules.

Work done (joules, J) = energy transferred
(joules, J)


Work done (joules, J) = force (newton, N) x…

Page 5

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When a car brakes, the kinetic energy is converted to heat energy
at the brakes and tyres:

Work done by brakes = initial kinetic energy (or loss)

F x d = ½ x m x v²

If the speed of the car is doubled, then the kinetic energy and

Page 6

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Energy is never created nor destroyed but only transferred from
one form to another.

Energy is only useful when it's transferred from one form to

The pendulum: gravitational potential energy is converted to kinetic
energy and back.

At the start the bob has no KE as it's not


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