Physics (Part-I) (UPSC)

Total Questions: 50

1. A parachutist jumps from a height of 5000 metre. The relationship between his falling speed, v and the distance fallen through d is best represented as: [1995]

Correct Answer: (d)
Solution:
  1. When a parachutist jumps, the initial motion is free fall, so the speed increases as the distance fallen increases.
  2. Air resistance also increases with speed, and eventually, a point is reached where the upward air resistance equals the downward gravitational force.
  3. After this point, the speed becomes constant—this is called terminal velocity.
  4. The graph showing this relationship starts with a rising slope (speed increasing with distance) and then flattens out (speed becomes constant) as distance increases.

So, the graph given in option (d) best represents the given situation.

2. Who among the following anticipated Newton by declaring that all things gravitate to the earth? [1995]

Correct Answer: (d) Brahmagupta
Solution:Brahmagupta, an Indian mathematician and astronomer who lived in the 7th century, wrote in his text Brahmasphutasiddhanta that "bodies fall towards the earth...because it is in the nature of the earth to attract bodies...".

This statement predates Isaac Newton's work on the law of universal gravitation by over a thousand years and demonstrates an early understanding of the concept of gravity.

3. A liquid is flowing in a streamlined manner through a cylindrical pipe. Along a section containing the axis of the pipe, the flow profile will be: [1996]

A liquid is flowing in a streamlined manner through a ...

Correct Answer: (a)
Solution:If a fluid flows such that its velocity at a point is always the same in magnitude and direction, the fluid is said to have a streamline flow. The type of flow in a fluid system is characterized by the presence of laminae, or parallel streams of fluid.

A streamline is a straight or curved path such that tangent to it at a point gives the direction of flow of liquid at that point. Thus, according to question the flow profile is best represented by figure (a).

4. The variation of displacement d with time / in the case of a particle falling freely under gravity from rest is correctly shown in graph: [1996]

Correct Answer: (a)
Solution:Graph (a) correctly represents the displacement-time relationship for a freely falling object. As time increases, the displacement increases quadratically due to constant acceleration under gravity. Remember, the key insight is that free fall leads to quadratic displacement with respect to time.

5. A simple machine helps a person in doing: [1996]

Correct Answer: (b) the same amount of work with lesser force.
Solution:A simple machine, such as a lever, pulley, or inclined plane, is a device that changes the direction or magnitude of a force.

It makes work easier by allowing you to apply a smaller force over a longer distance to achieve the same amount of work. It doesn't reduce the total work done, as work is defined as force multiplied by distance.

6. The tendency of a liquid drop to contract and occupy minimum area is due to: [1997]

Correct Answer: (a) surface tension
Solution:Surface tension is the cohesive force that exists at the surface of a liquid. It's caused by the attraction between the liquid molecules, which pulls them inward and makes the surface behave like a stretched elastic membrane.

This force minimizes the surface area of the liquid, which is why liquid drops in free fall, like raindrops, tend to form a spherical shape, as a sphere has the smallest surface area for a given volume.

7. Which one of the following is a vector quantity? [1997]

Correct Answer: (a) Momentum
Solution:Scalars are quantities that have magnitude only, they are independent of direction. Vectors have both magnitude and direction.

Momentum is the product of the mass and velocity of an object (p = mv) Momentum is a vector quantity, since it has a direction as well as a magnitude. The rest of quantities in option pressure, work and energy have magnitude but not direction.

8. A girl is swinging on a swing in sitting position. When the girl stands up, the period of swing will: [1997]

Correct Answer: (a) be shorter
Solution:The period of a simple pendulum (which a swing approximates) is determined by its length. The length of a pendulum is measured from the pivot point to the center of mass. When the girl stands up, her center of mass shifts upwards, closer to the pivot point of the swing.

This effectively shortens the length of the pendulum. Since the period of a pendulum is directly proportional to the square root of its length, shortening the length will decrease the period, causing the swing to oscillate faster.

9. A boy standing at the point O in the given diagram throws a ball three times with the same force, but projecting it along different inclinations from the ground. The results of the throws have been plotted in the diagram. Which one of the following is a valid conclusion? [1997]

Correct Answer: (d) The larger the initial inclination, the greater the height reached
Solution:The above diagram represents a body in projectile motion
Maximum height y max = (v² sin² θ)/(2g)
Thus, according to above equation greater the initial inclination, the greater is the height reached.

10. The working principle of a washing machine is: [1997]

Correct Answer: (a) centrifugation
Solution:A washing machine uses a process called centrifugation to separate water from the clothes. During the spin cycle, the drum rotates at a very high speed, creating a centrifugal force that pushes the clothes against the outer wall.
The water, being less dense, is forced out through the holes in the drum, leaving the clothes relatively dry.