A cyclist comes to a skidding stop in `10m`. During this process, the force on the cycle due to the road is `200N` and is directly opposite to the motion.
a. How much work does the road do on the cycle?
b. How much work does the cycle do on the road?

Explanation

(a) Work done by the road on the cycle is work done by the stopping frictional force on the cycle.
`W_(1)=F s costheta=(200)(10)cos180^(@)=-200J`
This is obviously negative.
(b) From Newton's third law, an equal and opposite force acts on the road due to the cycle.
`:.` Force on the road, `F=200N`.
But the road undergoes no displacement. Therefore, work done by the cycle on the road is zero.