A force P pulls on a crate of mass m that is in contact with a rough surface. The figure shows the magnitudes and directions of the forces that act on the crate in this situation. Wrepresents the weight of the crate. FN represents normal force on the crate, and f represents the frictional force.

A cardboard box rests on the floor of an elevator. The box has a mass m = 2.75 kg and the elevator has an upward acceleration of a.   a.  Write an expression for the sum of the forces acting on the box in the y-direction, ΣFy, given that up is the positive y-direction. Your answer should be in terms of FN, m, and g.  b. Write an expression for the normal force, FN, that the block experiences in terms of the elevator's acceleration, the block's mass, and the acceleration of gravity.  c.  If the elevator's acceleration has a magnitude of g in the downward direction, what would the normal force, FN1 be in Newtons?  d.If the elevator's acceleration had a magnitude of g in the upward direction, what would the normal force FN2 be in Newtons?

A teenager of mass m1 = 56 kg pushes backwards against the ground with his foot as he rides his skateboard. This exerts a horizontal force of magnitude F foot = = 18.5 N. The skateboard has m2 = 2.6 kg. a. Write an expression for the magnitude of the horizontal component of force that the ground exerts on the teenagers foot, F ground. b. Write an expression in terms to given quantities for the magnitude of the skateboard acceleration, a , while the teenager is pushing backwards on the ground? c. What is the numerical value of the magnitude of the acceleration, a, in m/s square?