physics

1) A cord is used to vertically lower an initially stationary block of mass M = 8.0 kg at a constant downward acceleration of g/2. When the block has fallen a distance d = 4.6 m, find (a) the work done by the cord's force on the block, (b) the work done by the gravitational force on the block, (c) the kinetic energy of the block, and (d) the speed of the block. (Note : Take the downward direction positive)

2) The only force acting on a 3.7 kg body as it moves along the positive x axis has an x component F_x = -3x N, where x is in meters. The velocity of the body at x = 2.6 m is 8.9 m/s. (a) What is the velocity of the body at x = 3.8 m? (b) At what positive value of x will the body have a velocity of 3.4 m/s?

3) A single force acts on a 2.6 kg particle-like object in such a way that the position of the object as a function of time is given by x = 4.3t - 2.3t² + 3.4t³, with x in meters and t in seconds. Find the work done on the object by the force from t = 0 to t = 9.0 s.