Physics question Dynamics forces and kinematics review

. A 38 kg crate rests on a horizontal floor. A horizontal pulling force of 170 N is needed to start the crate moving. After it is in motion, a horizontal pulling force of 120 N is needed to slide the crate across the floor at a constant speed. a. Find the coefficient of static friction between the crate and the floor. b. Find the coefficient of kinetic friction between the crate and the floor. A car is travelling at 18 m/s on a horizontal road. The driver of the car looks the wheels by slamming on the brakes. The coefficient of kinetic friction between the tires and the road is 0.62. Find the stopping distance of the car. Another elevator problem. A 4.8 kg suitcase is sliding across a horizontal floor of an elevator. The coefficient of kinetic friction between the suitcase and the floor is 0.28. a. if the elevator is moving upward at a constant speed of 1.6 We, find the kinetic frictional force acting on the suitcase. b. if the elevator is accelerating upwards at 1.6 m/s2, find the kinetic frictional force acting on the suitcase. c. if the elevator is accelerating downwards at 1.6 m/si', find the kinetic frictional force acting on the suitcase. A 3.2 kg chunk of wood is pressed between two hands. The forces, equal in magnitude, act on opposite sides of the block and are perpendicular to the chunk of wood. The coefficient of static friction between the hands and the wood is 0.53. Find the magnitude of the minimum pressing force exerted by each hand to keep the chunk of wood from falling. (Remember that the normal force is not always upwards)