HardPhysicsHigh School (9–10)GeneralMechanics › Work, Energy and PowerNumerical

A car of mass 1100 kg moves at 18 m/s. The brakes give a steady force of 4950 N against the motion.

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A car of mass $1100\ \text{kg}$ moves at $18\ \text{m/s}$ . The brakes give a steady force of $4950\ \text{N}$ against the motion.

How far does the car go before it stops?
How far does it go if it starts at $36\ \text{m/s}$ , with the same brake force?

Need a reminder? The key ideaShow

Kinetic energy $KE = \tfrac{1}{2}mv^2$ : twice the speed gives four times the energy. The work done on an object equals the change in its kinetic energy; a brake force $F$ stops it in $d$ when $F \times d = \tfrac{1}{2}mv^2$ .

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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A car of mass 1100 kg moves at 18 m/s. The brakes give a steady force of 4950 N against the motion.

The worked solution

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