Question

a 40kg boy runs up a flight of stairs which is 5m high in 5s. his power output is?
A. 200W
B. 392W
C. 1000W
D. 1568W
E. 2000W

Answer 1

Answer on Question #43274 – Physics – Mechanics | Kinematics | Dynamics

Question.

A 40kg boy runs up a flight of stairs which is 5m high in 5s. His power output is?

A. 200W

B. 392W

C. 1000W

D. 1568W

E. 2000W

Given:

$$\begin{array}{l} m = 40 \, kg \\ h = 5 \, m \\ t = 5 \, s \\ \end{array}$$

Find:

$$P = ?$$

Solution.

By definition the power is the rate of doing work:

$$P = \frac{A}{t}$$

$A$ is the work done;

$t$ is the time.

In our case, the work done is moving the boy against the forces of gravity. So,

$$A = m g h$$

$g = 9.8 \frac{m}{s^2}$ is the gravitational acceleration.

Therefore,

$$P = \frac{A}{t} = \frac{m g h}{t}$$

Calculate:

$$P = \frac{40 \cdot 9.8 \cdot 5}{5} = 392 \, W$$

Answer.

B. 392W

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