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9th Class Science Work and energy Question Bank Work and Energy

  • question_answer
    A boy of mass 50 kg runs up a flight of 120 stairs, each measuring a height of 25 cm, in one minute and 40 seconds. If \[g\text{ }=\text{ }10\text{ }m\text{ }{{s}^{-2}}\], the power of the boy is

    A) 150 W             

    B) 750 W 

    C)        500 W 

    D)        250 W

    Correct Answer: A

    Solution :

    Here, mass, m = 50 kg Height of the staircase, \[h=120\times \frac{25}{100}=30m\] Time taken to climb \[\text{= 1 min 40 sec = 100 s}\] We know, Power, P \[\text{=}\frac{\text{Work done}}{\text{Time taken}}=\frac{mgh}{t}\]                         \[=\frac{50\times 10\times 30}{100}=150W\]


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