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Consider the following two statements: Statement I: A truck and a car moving with the same kinetic energy are brought to rest by equal retarding forces. Both travel the same distance before stopping. Statement II: A car moving eastward turns and moves northward with unchanged speed. The acceleration of the car during the turn is zero. Choose the most appropriate conclusion.

1. Statement I is correct but Statement II is incorrect
2. Statement I is incorrect but Statement II is correct
3. Both Statement I and Statement II are incorrect
4. Both Statement I and Statement II are correct

Correct answer: Statement I is correct but Statement II is incorrect

Solution

Statement I: By the work-energy theorem, the retarding force F does work F*d to bring the vehicle to rest from kinetic energy KE. So F*d = KE. If KE and F are the same for both vehicles, then d = KE/F is the same. Statement I is CORRECT regardless of vehicle mass. Statement II: When the car changes direction (east to north) even at constant speed, the velocity vector changes direction. A change in velocity (even direction only) means there IS acceleration (centripetal acceleration). Statement II is INCORRECT.

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