6. (Work and Energy) A student in a geology lab lifts a rock, whose mass m is 12

Question

6. (Work and Energy) A student in a geology lab lifts a rock, whose mass m is 12 kg, from the floor and raising it (with negligible accelcration) to a height d of 1.8m, put it on a shelf. We wish to identify the forces that act on the rock and to calculate the work that they do. (a) Identify these forces and calculate their magnitudes.(1) (b) How much work does the student student do on the rock?(1) 2 (c) How much work does the earth's gravity do on the rock ?(1) (d) What is the total work done on the rock by all the forces that act on it?(1)

Explanation / Answer

A. As the acceleration is negligibke so net force on the object taken to be 0

So there are only two firces which are actong on the object

Gravitational force= mg= 12*9.8 = 117.6 N

And applied force= 12*9.8= 117.6 N

Both are directed opposite to each other.

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B. Workdone by applied force= mgh= 117.6*1.8= 211.68 J

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C. Workdone by gravity= - 117.6*9.8= - 211.68 J

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Net workdone

= 117.6*1.8 +(- 117.6*1.8)

= 0 J

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Comment in case any doubt..goodluck

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