Question

Power is the rate of doing work. To increase Power, based on the equation, we can increase the work and keep time constant, or keep work constant but decrease the time over which it is done. Imagine you are coming home after grocery shopping. You have 5 large, heavy grocery bags. You can take them all in one trip or you can take 2 trips. Answer the following questions.

1. Which scenario has greater work done, carrying all the bags in 1 trip or 2 trips? Why?
2. Which scenario has greater power, assuming 2 trips takes twice as long as 1 trip? Why?

Answer 1

Work done = (Force).(displacement)

Force required to lift the bags is directly proportional to the number of bags.

Let us consider weight of each bag to be 'W' and carried through a distance 'd'

If all 5 bags are carried in one trip, then work done is 5Wd.

If in 2 trips, let's say, 2 and 3 bags are carried in each trip, then total work done will be 2Wd + 3Wd = 5Wd.

We can see, work done in each scenario is same.

Power = Work/time

From above part, we saw that work done is same in both scenarios, 1 trip and 2 trips but time taken will be double in the scenario with 2 trips as 2 trips are to be made. As a result, power decreases to half in the scenario with 2 trips.

Scenario with 1 trip has greater power.