Physics

Problem

A motor delivers constant power of

200\,\text{W}

for

5\,\text{s}

to accelerate a

10\,\text{kg}

cart that starts from rest on a smooth track. What is the speed of the cart at the end of

5\,\text{s}

? a)

20\,\text{m/s}

14\,\text{m/s}

28\,\text{m/s}

10\,\text{m/s}

Intuitive explanation

The key insight is that constant power means the force changes as the cart speeds up—unlike constant force problems. Use the work–energy theorem: the work done by the motor equals the change in kinetic energy. Since $P = W/t$ , you can find total work directly from power and time, then solve for the final speed using $W = \frac{1}{2}mv^2 - 0$ .

Intuitive explanation

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