UPSC Prelims 2008 · General Studies
Question 127: Science and Technology
A person is sitting in a car which is at rest. The reaction from the road at each of the four wheels of the car is R. When the car runs on a straight level road, how will the reaction at either of the front wheels vary?
AnswerThe answer is (c).
On a straight level road at steady speed the car is not accelerating up or down and the loads are not changing, so the weight is shared among the wheels as before and each front wheel carries the same reaction R. Only if the car accelerated or braked would weight shift between the front and rear wheels. The road's material affects friction, not the vertical reaction here.
Why each option is right or wrong
- (a) A reaction above R would appear under braking, not steady motion.
- (b) A reaction below R would appear under acceleration, not steady motion.
- (c) At steady speed the front reaction stays equal to R.
- (d) The road's material affects friction, not the vertical reaction.
Worth knowing: The question does not say the car moves at constant speed; the answer assumes it does, since acceleration would shift load to the rear wheels.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2008, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.