A workshop crane lifts the same crate in two consecutive stages

PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials

Problem

A workshop crane lifts the same crate in two consecutive stages. Stage A: The crate is raised through

12\,\text{m}

, and

48\,\text{kJ}

of work is done while the crane delivers a constant power of

800\,\text{W}

. Stage B: Without pause, the crate is lifted a further

8\,\text{m}

, and an additional

32\,\text{kJ}

of work is done while the power output rises to

1.6\,\text{kW}

. (i) Determine the time taken by the crane in Stage A. (ii) Determine the time taken in Stage B. (iii) Calculate the total time to raise the crate through the full

20\,\text{m}

distance. (iv) Compute the average power developed over the entire lifting process.

Related theory

Power
Work, Energy and Power
Power (rate of doing work)
Work and Energy

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