A man sitting on a 1.4m ledge carefully lowers a 4kg object with a rope so that

Question

A man sitting on a 1.4m ledge carefully lowers a 4kg object with a rope so that it comes to a stop when it reaches the ground. Let your system be the Earth and the object (but not the man). For the time between when the object starts downward, at a speed of 1 m/s, and when it reaches the ground (with zero velocity), answer the following questions:/

Has the man done any work on the object? Explain?

What external forces are acting on the object as it falls? (recall that the Earth is in the system)

What are the changes in the kinetic energy and potential energy of the system? What is the work done?

Explanation / Answer

Yes the man has done the work, because man is acting force on the object opposite to gravity i.e. mg plus extra force that is decelerating the object. And ys there is displacement of 1.4m, so work is dine by him

External forces acting on object are:-

Downward gravitational force and upward force by the man

Initially velocity was 1m/s

Finally it becomes zero

So change in KE=0.5mv2=2J

Work done =mgh+change in KE=4*9.8*1.4 +2=56.88J

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