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A car of mass 1000 kg is travelling at 15 m/s. The driver applies the brakes for 4 seconds, slowing the car to 5 m/s. What is the average power output of the brakes over the 4 seconds? Assume there are no other forces acting on the car.

Kinetic Energy, EK=(1/2)mv². Energy is conserved, so the work done by the brakes, W, must be equal to the change in kinetic energy of the car, ∆EK. Therefore: W = ∆EK = (1/2)1000(15

Answered by Adam H. • Physics tutor

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If a box full of feathers and a box full of bricks were to be dropped at the same time and from the same height, which one would hit the ground first?

They would hit to ground at the same time. This is because they would both accelerate to the ground at 10m/s^2 due to gravity regardless of what their mass is. This is contrary to one might intuit when co...

Answered by Adam Yanis C. • Physics tutor

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Which is heavier, a ton of feathers or a ton of lead?

They're both the same. The feathers would take up a lot more space though! Feathers have a lower density than lead (i.e. for the same volume, feathers are less heavy). In practice, if you drop a tonne of ...

Answered by Francis N. • Physics tutor

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Define Newton's three laws

1st Law - a body will move with constant velocity or remain at rest unless acted on by a resultant force
2nd Law - F = ma. The rate of change of momentum of an object is equal to the resultant force ...

Answered by George W. • Physics tutor

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