Question

Two robbers are sliding a 225 kg safe a displacement of 8.5 m straight toward their truck. The push of the first robber is 12 N, directed at an angle of 30 degrees below the horizontal. The pull of the second robber is 10 N directed at 40 degrees above the horizontal. a) What is the net work done on the safe during the displacement? b) During the displacement, what is the work done on the safe by the force of gravity? c) The safe is initially stationary. What is its speed at the end of the displacement?

Answer 1

(a)The net work done will be given by,

Here F_net is the total force acting along the direction of displacement and it is given by,

Therefore the net work done on the safe is,

(b) Since the force of gravity is acting perpendicular to the direction of displacement, the work done due to gravitational force is 0.

(c) By law of conservation of energy we can say that the work done on the safe is converted to kinetic energy of the safe, So, (initial energy is 0)

Substituting we get,