** 12. A girl pushes horizontally cient of kinetic friction between the crate and the floor is 0.2; the coefficient of static friction is 0.4. on a 100-kg crate, as shown in the two figures below. The coeffi- a) For each of the two situations described in the figures, indicate whether the frictional force is static or kinetic. b) In each case, find the magnitude of the frictional force. Case 1: The girl is pushing with a force of 300 N, and the crate does not move. Case 2: The girl is pushing with a force of 300 N, and the crate is moving along the floor.

A sled weighing 53.5 N is pulled horizontally across snow so that the coefficient of kinetic friction between sled and snow is 0.100. A penguin weighing 70.5 N rides on the sled, as in the figure below. If the coefficient of static friction between penguin and sled is 0.700, find the maximum horizontal force that can be exerted on the sled before the penguin begins to slide off.

A 6 kg piece of wood is locked at rest on a given horizontal surface. a. Draw all forces acting on the wood, and calculate the magnitude of each force if µs = 0.6

A 1.2 kg block is moving down an inclined plane with constant velocity. The inclined plane makes an angle of 30 degrees with the horizontal. a. Find the normal force and the force of friction  b. What is the coefficient of friction between the block and the surface?