Work and Energy...

A rigid body of mass $$m$$ kg is lifted uniformly by a man to a height of one metre in $$30$$ sec. Another man lifts the same mass to the same height in $$60$$ sec. The work done on the body against gravitation in both the cases are in ratio:

What is work done in holding a body of mass $$20\ kg$$ at a height of $$2\ m$$ above the ground? $$(g = 10\ m/s^2)$$

The law of conservation of energy implies that the:

In which one of the following cases is work done the maximum ?

How fast should a girl of 40 kg run so that her kinetic energy is 320J?

A vehicle travelling at $$30 \ m/s$$ stops at a distance of $$50 \ m$$ decelerating uniformly. A force of $$9000 \ N$$ is exerted on it by the brakes. What is the work done by the brakes?

Work done by static friction force when a person starts running is .......... .

Which one of the following possesses kinetic energy?

Energy conservation law says that:

A body at rest have: