A couple of questions:(adsbygoogle = window.adsbygoogle || []).push({});

1. Why can't we tell what force a 10 N rock exerts on the ground when dropped from 10 m?

If a car is moving at constant velocity, it's net force is 0, but it is still doing work. How?

2. Work = force * distance, Kinetic energy = 1/2 mass * velocity^{2}, Force * distance = 1/2 mass * velocity^{2}

3. For the first question, I think a valid solution would be that we don't know the acceleration because the problem doesn't tell us to assume we're on earth. However, I think that's kind of a cop out. A more realistic answer might be that we don't know the distance over which the rock exerts force on the ground: The work is 100 J, and if divided by the distance, we would get the force, right?

For the second question, is this a question about what system we're talking about? Because if the car is the system, it is doing exerting force, but if our system is the car and the road, then the car's force and the frictional force cancel for a net force of zero, allowing the car to move at a constant velocity. So if the net force is 0 N, then the work (Force * distance) should be 0 J. But clearly the car is doing work, because it's kinetic energy is 1/2 mass * velocity^{2}. I'm not exactly sure how to reconcile the two equations.

Thanks!

~ Adhish

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# Homework Help: Work/Energy vs. Force Questions

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