17. a 25 kg block is initially at rest on a rough, horizontal surface. a horizontal force of 75 n is required to set
the block in motion, and a 60 n force is required to keep it in motion at a constant speed once it is moving.
what are the coefficients of static and kinetic friction?

22. the top of a cliff is located a distance h above the ground. at a distance h/2 there is a branch that juts out from the side of the cliff, and on this branch a bird's nest is located. two children throw stones at the nest with the same initial speed, one stone straight downward from the top of the cliff and the other stone straight upward from the ground. in the absence of air resistance, which stone hits the nest in the least amount of time?