how can work be done when the net force equals zero? Explain?

Question

we learned that the net force is zero for a car traveling along a level road at constant velocity, and in this chapter we learned that work is done in such a case. Your friend asks “how can work be done when the net force equals zero? Explain

Answer 1

Remember that there is friction acting on the car from the movement of the wheels over the road. Work must therefore be done to overcome this friction.

Answer 2

Consider this. 2 men pull a rope with all their strength. Let's assume that they both have the same strength. Obviously, they won't move a centimeter from the spot that they first started on. But after 10 or so minutes, they'll be tired. Why? Well, they both worked.

Same thing with a car. It must overcome wheel-to-road friction, air resistance, internal engine work loss and so forth. The car applies a force that has to counter the opposing forces. In this aspect, the car 'works'. However, since the car neither accelerates, nor decelerates, all the work is lost to 'negative work' executed by ate above mentioned factors. The useful work is 0, but the raw work is greater than 0.

Answer 3

Key word is "net". Which means all forces balance if nf=0.
The work therefore would be whatever force it takes to exactly overcome (balance) gravity and friction which keeps the car at constant velocity. Otherwise, it would roll to a stop even on a level road.

nf = 0 .......... constant velocity, work = +
nf = + ........... acceleration, work = +
nf = - ........... deceleration, work = + or -

Answer 4

Think of it in terms of energy. The frictional force felt by the car from the road surface is non-conservative (energy is lost due to friction). In order to conserve energy and maintain a constant speed, your car must do work.

Answer 5

If the net force is zero, I don't work is possible in that case.

F=ma

work = F x distance