Question

Bob (88 kg) jumps out of a plane, starting at rest. After falling for 1 km, he is moving downward at 96 m/s. How much work is done by friction over this distance? You may assume that the only forces are gravity and friction.

Answer 1

Answer:

The work done by friction is 456 kJ.

Explanation:

Given that,

Mass of Bob, m = 88 kg

After falling for 1 km, he is moving downward at 96 m/s. It is required to find the work done by friction over this distance. It can be calculated using work energy theorem as :

$mgh+W=\dfrac{1}{2}mv^2\\\\W=\dfrac{1}{2}mv^2-mgh\\\\W=m(\dfrac{1}{2}v^2-gh)\\\\W=88\times (\dfrac{1}{2}\times (96)^2-9.8\times 1000)\\\\W=-456896\ J\\\\W=-456\ kJ$

So, the work done by friction is 456 kJ. Hence, this is the required solution.