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:When a parachutist jumps from a height, its speed first increases with the distance fallen and then becomes constant. So, the graph given in option (d) best represents the given situation.

New NCERT, Science- Class 9, Chapter-8, Motion, Speed with Direction from Page no.-101.

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

(a) Aryabhatta
(b) Varahamihira
(c) Buddhagupta
(d) Brahmagupta

Correct Answer: (d) Brahmagupta

Solution:Brahmagupta anticipated Newton by declaring that all things gravitate to the earth.

Brahmagupta (born 628 A.D.) who lived at Ujjain, then a great astronomical center of India was aid to be great pioneer of encyclopedic knowledge, he was a more original thinker who separated astronomy from astrological speculations.

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]

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]

(a) less work.
(b) the same amount of work with lesser force.
(c) the same amount of work slowly.
(d) the same amount of work much faster.

Correct Answer: (b) the same amount of work with lesser force.

Solution:A simple machine is a mechanical device that changes the direction or magnitude of a force. In general, they can be defined as the simplest mechanisms that use mechanical advantage to multiply force.

Thus, simple machine helps us in doing same amount of work with lesser force. Few examples of simple machines are pulley, lever, wheel, screw, etc.

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

(a) surface tension
(b) viscosity
(c) density
(d) vapour pressure

Correct Answer: (a) surface tension

Solution:It is observed that liquid drop tend to contract and appear spherical when it is set free from external forces like gravity, etc. Surface tension is the property among liquids due to which they tend to occupy minimum surface area. That's why water droplet appears spherical because for a given volume, a sphere has minimum surface area. Due to this property of surface tension liquid surface stretches and behaves like a stretched membrane.

Surface tension in water might be good at performing tricks, such as being able to float a paper clip on its surface, but surface tension performs many more duties that are vitally important to the environment and people.

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

(a) Momentum
(b) Pressure
(c) Energy
(d) Work

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]

(a) be shorter
(b) be longer
(c) depends on the height of the girl
(d) not change

Correct Answer: (a) be shorter

Solution:Effective length is the length of point of suspension to the centre of gravity(mass) of a body. Let it be & when the girl is sitting and l' when girl stands up. Here l > l' Thus, the time period of swing will decrease because time period of swing is given by formula - T = 2pi * sqrt(l/g)

So, it is clear from above formula that the time period of system is directly proportional to effective length.

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]

(a) The larger the initial inclination, the longer the throw
(b) The larger the height reached, the longer the throw
(c) The larger the height reached, the shorter the throw
(d) The larger the initial inclination, the greater the height reached

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]

(a) centrifugation
(b) dialysis
(c) reverse osmosis
(d) diffusion

Correct Answer: (a) centrifugation

Solution:Washing machine works on the principle of centrifugation. Centrifugation is a process that involves the use of the centrifugal force for the separation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture migrate towards the axis.

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