6. Intro to Forces (Dynamics)

Which of the following statements about dynamics is correct?

A $100\mathrm{kg}$ rock is in space, far from any planets, stars or black holes. It is moving in a straight line at a constant $\mathrm{10,000}\mathrm{m}/\mathrm{s}$ relative to our sun. What total force is required to keep it moving that fast?

An elevator is going up at a constant speed in a very tall building. Assume the only forces acting on the elevator are a downward weight force and the force of a cable pulling the elevator up. Ignore air resistance and friction. How does the magnitude of the weight force compare to the magnitude of the force of the cable?

A $10\mathrm{N}$ horizontal force is applied to a $10\mathrm{kg}$ box causing it to speed up. The force of kinetic friction is $5\mathrm{N}$. Which choice best describes the subsequent motion of the box?