Question

1.Two cars have the same weight, but one of the cars has an engine that provides twice the power of the other. Which car can make it to the top of a mountain pass first? which car does move work to reach the pass?
2.You carry two heavy bags of groceries upstairs to your kitchen. Will you do more work on the bags if you carry them up one at a time ? explain.
3. How much does a 25-newton force do to lift a potted plant from the floor to a shelf 1.5 meters high?
4. You lift a large bag of flour from the floor to a 1 meter high counter, doing 100 joules of work in 2 seconds. How much power do you use to lift the bag of flour?

Answer 1

1. The car with twice the engine power will reach the top first (it can deliver the required energy faster). Both cars, however, must do the same mechanical work to climb to the same height (neglecting friction and air resistance): W = m g h. The difference is the time: t = W/P, so doubling P halves the time.

2. No — the total mechanical work against gravity is the same either way. Each bag is lifted by the same height, so total work = (m1 + m2) g h whether you carry them together or one at a time. (Practical note: your muscles may expend more metabolic energy carrying one at a time because of inefficiencies, extra walking, posture changes, etc., but the physics work against gravity is unchanged.)

3. W = F · d = 25 N × 1.5 m = 37.5 J (positive work done to lift the plant).

4. Power = work / time = 100 J / 2 s = 50 W (average power used).