A 1000-N crate is being pushed across a level floor at a constant speed by a force F of 300 N at an angle of 20.0 degrees below the horizontal, as shown in Figure P4.41a. (a) What is as the coefficient of kinetic friction between the crate and the floor? (b) If the 300-N force is instead pulling the block at an angle of 20.0 degrees above the horizontal, as shown in Figure P4.41b, what will be the acceleration of the crate? Assume that the coefficient of friction is the same as that found in part (a).

Answer 1

component of push along floor = 300 cos 20
component of push normal to floor = 300 sin 20
friction force holding back = (1000 + 300 sin 20) * mu
300 cos20 = mu (1000 + 300 sin 20)
solve for mu

then I am sure you can do the rest.