EWT | Academic Question

Questions
Question (1)
QN0035070

A ball is travelling with uniform translatory motion. This means that

  • (A)

    it is at rest

  • (B)

    the path can be a straight line or circular and the ball travels with uniform speed

  • (C)

    all parts of the ball have the same velocity (magnitude and direction) and the velocity is constant

  • (D)

    the centre of the ball moves with constant velocity and the ball spins about its centre uniformly

Correct Answer: C
Explanation:

In a uniform translatory motion if all the parts of the body moves with (same velocity in same straight line, so the velocity is constant.

The situation is shown in (figure) where a body  is in unfirom translatory motion.

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Question (2)
QN0035071

A metre scale is moving with uniform velocity. This implies.

  • (A)

    the force acting on the scale is zero, but a torque about the centre of mass can act on the scale 

  • (B)

    the force acting on the scale is zero and the torque acting about centre of mass of the scale is also zero

  • (C)

    the total force acting on it need not be zero but the torque on it is zero

  • (D)

    neither the force nor the torque need to be zero

Correct Answer: B
Explanation:

According to question we have to apply Newton's second law of motion, in terms of force and change in momentum.

We know that

As given that the meter scale is moving with uniform velocity, hence

Force

No change in its velocity i.e., acceleration of it zero by

Newton's second law.

Hence, net or resultant force must act on body is zero:

, so,

As all part of the scale is moving with uniform velocity and total force is zero, hence, torque will also be zero.

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Question (3)
QN0035072

A cricket ball of mass  has an initial velocity  and a final velocity , after being hit. The change in momentum (final momentuminitial momentum) is (in )

  • (A)

    zero

  • (B)

  • (C)

  • (D)

Correct Answer: C
Explanation:

As given that,

Mass of the ball

Change in momentum

Final momentum - Initial momentum

Hence verifies option (c).

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Question (4)
QN0035073

In the previous problem (3), the magnitude of the momentum transferred during the hit is

  • (A)

    zero

  • (B)

  • (C)

  • (D)

Correct Answer: C
Explanation:

From previous solution

Magnitude of

Verifies the option (c).

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Question (5)
QN0035074

Conservation of momentum in a collision between particles can be understood from 

  • (A)

    Conservation of energy

  • (B)

    Newton's first law only 

  • (C)

    Newton's second law only

  • (D)

    both Newton's second and third law

Correct Answer: D
Explanation:

From the FBD

and

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Question (6)
QN0035075

A hockey player is moving northward and suddenly turns westward with the same speed to avoid an opponent. The force that acts on the player is            

  • (A)

    frictional force along westward

  • (B)

    muscle force along southward

  • (C)

    frictional force along sotuh-west

  • (D)

    muscle force along south-west

Correct Answer: C
Explanation:

Consider the adjacent diagram.

The force on player is due to rate of change of momentum.

The direction of force acting on player will be the same as the direction of change in momentum.

Let i.e., Initial momentum of player northward  i.e., Final momentum of player towards west.

Clearly,

Change in momentum

= Clearly resultant  will be along south-west.

So, it will be also the direction of force on player.

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Question (7)
QN0035076

A body of mass  travels according to the law   where,  and . The force acting on the body at  is 

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: A
Explanation:

As given that, mass

As given equation is

Force acting on body .

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Question (8)
QN0035077

A body with mass  is acted upon by a force . If its initial velocity at  is , the time at which it will just have a velocity along the -axis is

  • (A)

    never

  • (B)

  • (C)

  • (D)

Correct Answer: B
Explanation:

As given that mass

Acting force

Initial velocity at

Retardation,

As the final velocity along -component only. So its  component must be zero.

From , for -component only,

. Hence verifies the option (b).

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Question (9)
QN0035078

A car of mass  starts from rest and acquires a velocity along east,  in two seconds. Assuming the car moves with uniform acceleration, the force exerted on the car is      

  • (A)

    eastward and is exerted by the car engine

  • (B)

    eastward and is due to the friction on the tyres exerted by the road

  • (C)

    more than  eastward exerted due to the engine and overcomes the friction of the road

  • (D)

    exerted by the engine

Correct Answer: B
Explanation:

As given that mass of the car

As car starts from rest,

Velocity acquired along east

Time .

We know that,

(Force, by engine is internal force)

Hence, force acting on the car is  towards east due to force of friction is  which moves the car in eastward direction. Hence, force by engine is internal force.

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