A man of mass \(m,\) standing at the bottom of the staircase, of height \(L,\) climbs it and stands at its top.
| (a) | work done by all forces on man is equal to the rise in potential energy \(mgL.\) |
| (b) | work done by all forces on man is zero. |
| (c) | work done by the gravitational force on man is \(mgL.\) |
| (d) | the reaction force from a step does no work because the point of the application of the force does not move while the force exists. |
Choose the correct option:
1. (a), (d)
2. (a), (c)
3. (b), (d)
4. (a), (b), (c)
(b, d) Hint: Apply the work-energy theorem and the concept of work.
Step 1: Find the work done by all the forces.
When a man of mass m climbs up the staircase of height L work done by the gravitational force on the man is-mgl work done by internal muscular forces will be mgL as the change in kinetic energy is almost zero.
Hence, total work done = -mgL + mgL = 0
Step 2: Find the work done by contact force.
As the point of application of the contact, forces do not move hence work done by reaction forces will be zero.
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