UPSC Prelims 2003 Q37: Science & Technology – Physics
An oil tanker is partially filled with oil and moves forward on a level road with uniform
acceleration. The free surface of oil then
- (a) Remains horizontal
- (b) Is inclined to the horizontal with smaller depth at the rear end
- (c) Is inclined to the horizontal with larger depth at the rear end
- (d) Assumes parabolic curve
Answer: (c) Is inclined to the horizontal with larger depth at the rear end
Explanation
Free surface of oil in an accelerating tanker
| Condition | Effect |
|---|---|
| Tanker accelerates forward | Oil experiences a backward pseudo-force |
| Surface | Tilts, rising towards the rear |
| Depth | Larger at the rear end, smaller at the front |
As the tanker accelerates forward, the oil is pushed backwards relative to the tanker, so its free surface is inclined with the larger depth at the rear end.
Answer: (c) Is inclined to the horizontal with larger depth at the rear end.
Why each option is right or wrong
- (a) Incorrect. The surface cannot stay horizontal under acceleration.
- (b) Incorrect. The depth is larger, not smaller, at the rear.
- (c) CORRECT. Oil piles up at the rear end.
- (d) Incorrect. A parabola occurs for rotation, not linear acceleration.
Key point
Linear acceleration a: the surface tilts at angle tan = a/g, rising at the back.
Remember
Accelerating forward makes the oil pile up at the rear.
Common mistakes
- Placing the larger depth at the front.
- Confusing linear acceleration with rotation (parabolic surface).
- Forgetting the inertia of the liquid.
Exam tip
Think of a glass of water in a braking or accelerating car.
Sources
- NCERT Class XI Physics — Mechanical Properties of Fluids
- NCERT Class XI Physics — Laws of Motion