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Coefficient of friction, momentum, speed and distance

I have some physics questions:

1. It takes a force of 300 N to keep a 500-N box sliding across a floor. What is the coefficient of the sliding friction?
2. A force acting on a 5.0-kg body increases its speed uniformly from 2.0m/s to 8.0m/s in 3 s. What is the initial momentum of the body? What is the final momentum of the body? What is the force acting on it?
3. In order to swing a .1kg mass tied to one end of a cord in a horizontal circle of radius .5 m so that its tangential speed is .2m/s what centripetal force must you exert on the mass through the cord?
4. At what distance from the center of the earth does g = 2.0 m/s x s (s squared)

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If 300N is the minimum force required to keep an object from moving, then it is also the maximum amount of force caused by friction. As a result, we can say that:

Force of friction = coefficient of friction x normal force of object = 300N
Ff = uN = 300

The normal force, assuming that the object is sitting flatly on a surface, is exactly equal to that of the force of gravity. This is because gravity on a still object causes the object to push down onto the surface where it rests, and there is an equal and opposite force - the normal force from the surface. We know the object is 500N in weight, and thus, again if sitting flatly, so ...

Solution Summary

Coefficient of friction, momentum, speed and distance are examined.