Question 21

To maintain a speed of $$80$$ km h$$^{-1}$$ by a bus of mass $$500$$ kg on a plane rough road for $$4$$ km distance, the work done by the engine of the bus will be _____ kJ. [The coefficient of friction between tyre of bus and road is 0.04]

Correct Answer: 800

$$f_k = \mu mg$$

$$f_k = 0.04 \times 500 \times 10 = 200 \text{ N}$$

$$W = f_k \times d$$

$$W = 200 \text{ N} \times 4000 \text{ m} = 800,000 \text{ J}$$

$$W = 800 \text{ kJ}$$

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