Acave rescue team lifts an injured spelunker directly upward and out of a sinkhole by means of a motor-driven cable. the lift is performed in three stages, each requiring a vertical distance of 10.0 m:
(a) the initially stationary spelunker is accelerated to a speed of 5.00m/s;
(b) he is then lifted at the constant speed of 5.00m/s;
(c) finally he is decelerated to zero speed. how much work is done on the 80.0kg rescuee by the force lifting him during each stage?

a) 8.85 kJ

b) 7.85 kJ

c) 6.85 kJ

Explanation:

we will use the energy conservation theorem for all of the stages

for stage 1:

the initial velocity and the potential gravitational energy at the bottom is zero:

for stage 2:

the velocity is constant so there is no change in the kinetic energy, so there is change only on the potential gravitational energy:

for stage 3:

there is a change for both, gravitational and kinetic energy so:

because if the tool that you are using is not balanced it there would be false mass.