It takes 20 s for girl A to climb up the stairs while girl B takes 15 s for the same job. Compare : (i) the work done and (ii) the power spent by them.

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Solution

a) Let h be the height of the staircase climbed by A and B.
Let m_A be the weight of A and m_B is the weight of B.

Work done by A to climb the Staircase, W_A = m_A×g×h Joules

Work done by B to climb the Staircase W_B = m_B×g×h Joules

Hence the ratio W_A/W_B = m_A / m_B

b) Power developed by A, P_A = (m_A×g×h)/20 watts
Power developed by B, P_B = (m_B×g×h)/15 watts

Power ratio P_A/P_B = (15m_A)/(20m_B) = (3m_A)/(4m_B)

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