# General Science - Physics MCQs

Physics Objective (Multiple Choice) General Knowledge & General Science Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examinations.

21. Which of the following is/are independent of mass during the projectile motion?

[A] Time of Flight

[B] Horizontal Range

[C] Maximum Height

[D] All of the above

Show Answer

**Correct Answer:** D [All of the above]

**Notes:**

The Time of Flight, Horizontal Range and the Maximum Height of an object are independent of mass of the object during the projectile motion.

22. Which of the following statements regarding vectors is NOT correct?

[A] A unit vector is dimensionless

[B] A vector cannot be divided by a vector

[C] A vector changes, when it is displaced to itself

[D] Current is not a vector quantity

Show Answer

**Correct Answer:** C [A vector changes, when it is displaced to itself]

**Notes:**

A unit vector is unit less and dimensionless. A vector cannot be divided by a vector as a vector cannot be divided by a direction. A vector does not change, when it is displaced to itself. Time, Pressure, Surface Tension, Current are some of the quantities that have direction but are not vectors. A physical quantity is a vector only when it follows commutative law of addition of vectors.

23. Which of these is the cause of Friction?

[A] Roughness of surfaces in contact

[B] Force of adhesion between the molecules of the surfaces in contact

[C] Both a and b

[D] None of the above

Show Answer

**Correct Answer:** C [Both a and b]

**Notes:**

Friction is the force that opposes the relative motion between the two surfaces of objects in contact. Friction is caused due to: 1. Roughness of surfaces in contact 2. Force of adhesion between the molecules of the surfaces in contact

24. The Newton’s third law is applicable when:

[A] bodies are at rest

[B] bodies are in motion

[C] bodies are in the air

[D] bodies are at rest or in motion

Show Answer

**Correct Answer:** D [bodies are at rest or in motion]

**Notes:**

The Newton’s third law is applicable whether the bodies are at rest or in motion. It states that to every action there is an equal and opposite reaction.

25. The apparent weight of the body becomes zero in which of the following cases in the elevator?

[A] during free fall of a body under gravity

[B] when elevator is accelerating downwards

[C] when elevator is at rest

[D] when elevator is accelerating upwards

Show Answer

**Correct Answer:** A [during free fall of a body under gravity]

**Notes:**

The apparent weight of the body becomes zero in an elevator during free fall of a body under gravity. It can be said that the body becomes weightless as the force of reaction between the person and the plane with which he is in contact vanishes.

26. The thrust on the rocket is:

[A] in the same direction of the rocket

[B] in the opposite direction of the rocket

[C] at 90° to the direction of the rocket

[D] None of the above

Show Answer

**Correct Answer:** B [in the opposite direction of the rocket]

**Notes:**

The thrust on the rocket is in the opposite direction of the rocket. The thrust is the force with which rocket moves upwards. F = -u (dm/dt)

27. Which of the following is an example of application of force?

[A] when a body at rest starts moving

[B] when a moving body stops

[C] when moving body changes its direction

[D] All of the above

Show Answer

**Correct Answer:** D [All of the above]

**Notes:**

Force can be defined as an external effort in the form of push or pull which: (i) Produces or tries to produce motion in a resting body (ii) Stops or tries to stop a moving body (iii) Changes or tries to change the direction of motion of the body

28. Which of the following is NOT correct about an inelastic collision?

[A] Linear momentum is conserved

[B] Kinetic energy is conserved

[C] Total energy is conserved

[D] Some or all the forces involved may be non-conservative in nature

Show Answer

**Correct Answer:** B [Kinetic energy is conserved]

**Notes:**

Following are the basic characteristics of an inelastic collision: 1. Linear momentum is conserved 2. Kinetic energy is NOT conserved 3. Total energy is conserved 4. Some or all the forces involved may be non-conservative in nature

29. What is the dot product of two perpendicular vectors?

Show Answer

**Correct Answer:** B [0]

**Notes:**

When two vectors are perpendicular to each other, then θ = 90° and Cos 90° = θ . Therefore, A.B = A x B x Cos θ = A x B x Cos 90° = θ When two vectors are parallel to each other, then θ = θ ° and Cos θ ° = 1. Therefore, A.B = A x B x Cos θ = A x B x Cos θ ° = AB When two vectors are anti-parallel to each other, then θ =180° and Cos 180° = -1. Therefore, A.B = A x B x Cos θ = A x B x Cos 180° = -AB

30. Work done is defined as the dot product of which of the following vectors?

[A] Force and acceleration

[B] Force and area

[C] Force and instantaneous velocity

[D] Force and displacement

Show Answer

**Correct Answer:** D [Force and displacement]

**Notes:**

Work done is defined as the dot product of Force vector and displacement vector. W = F.s Work done is a scalar quantity. Note: Instantaneous power is defined as the dot product of Force vector and instantaneous velocity.

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