A girl with 50 kg mass climbs up a rope through a height of 5 metres. She takes 25 s to accomplish the task. What is the power (in watts) expended by the girl?
98
Power measures how fast work is done and is defined as work divided by time, \(P=\dfrac{W}{t}\).
When the girl climbs the rope, she does work against gravity by raising her body weight through a height, so the work done is \(W=mgh\).
The given data are mass \(m=50\ \text{kg}\), height \(h=5\ \text{m}\), time \(t=25\ \text{s}\), with \(g=9.8\ \text{m/s}^2\).
Work done: \(W=50\times 9.8\times 5=2450\ \text{J}\).
Power: \(P=\dfrac{2450}{25}=98\ \text{W}\).
The key concept is that gravitational potential energy gained per unit time equals the power expended.
Hence, the power expended by the girl is 98 watts.
Important Questions from Work Power Energy
Which of the following is NOT correct regarding friction?
If a pump can raise 200 liters of water through a height of 300 meters in one minute, how much work can it do in one hour?
Which of the following is an example of kinetic energy?
How much kinetic energy does a 160 g cricket ball have when it is thrown at a speed of 22 m/s?
The movement of birds is an example of _______.
