A car is stopped by a steady brake force of 750 N.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A car is stopped by a steady brake force of . It moves while it stops.
- How much work does the brake force do on the car?
- Why is the sign of this work negative?
Need a reminder? The key ideaShow
Work when an object moves a distance along a steady force ; . The work is positive when the force is along the motion, negative when it is against it, and zero when it is at right angles or nothing moves.
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.
Step 1. (a) The force is against the motion, so the work is negative: .
Step 2. (b) The brake pushes backward while the car moves forward. Negative work takes kinetic energy away, so the car slows and stops.
Answer: (that is, ).
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