A 40-N crate rests on a rough horizontal floor. A 12-N horizontal force is then applied to it. If the coefficients of friction are ls = 0.5 and uk = 0.4, the magnitude of the frictional force on the crate is:

An object of mass 3 kg moves towards the negative x axis with a constant speed of 8 m/s and the coefficient of kinetic friction of the object with the ground is 0.39, so the value of the net force on the box is:

Bob borrows a lunch tray of negligible mass to push Will on the tray across a level portion of the field. The coefficient of kinetic friction between the tray and the grass is 0.25 and the coefficient of static friction is 0.30. Will is pushed 40m across the field by Bob at a constant speed, but Bob is so tall that he pushes with a force of 40 degrees below the horizontal. Will gained some weight during quarantine, so he now weighs 120kg. a) What power does Bob need to move Will across the field in 20sec? b) What could Bob do to decrease the work he needs to push Will across the field without decreasing his force?

15. A force F-25 N that makes an angle @-37 with the horizontal moves a block of mass m-10 kg placed on a rough horizontal surface. The coefficient of kinetic frictional force between the block and the surface is p0.1. What is the magnitude of the kinetic frictional force (fa) in N? (a) 2.5 (b) 4.0 (e) 5.5 (b) 80 (d) 7.0 (c) 100 16. A block of mass m-7 kg is held stationary by a horizontal force F pressing it against a rough vertical wall coefficient of static friction between the block and the wall .=0.5, what is the minimum magnitude of the force F in N required to keep in the figure. IF the it stationary? (a) 60 (e) 140 (e) 8.5 (d) 120 m