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Q:

A man stands in a lift which accelerates upwards. The resultant reaction force on the floor of the lift is 

A) greater than the weight of the man B) less than the weight of the man
C) Same as the weight of the man D) Zero

Answer:   A) greater than the weight of the man



Explanation:

The weight of the man mg is acting on the floor. As the lift is moving up with an acceleration, say a, the man too in it is having this acceleration. The force producing this acceleration is ma. By Newton's third law, this force will have an equal reaction pressing the floor equal to ma. Therefore the total resultant reaction on the floor is mg+ma = m(g+a) which is mg, the weight of the man. So (a) is correct.

Subject: Physics
Q:

What is the full form of "RADAR" ?

A) Radio Detecting and Ranging B) Region Device and Ranging
C) Radio Detect and Rangs D) Radio Device and Ranging
 
Answer & Explanation Answer: A) Radio Detecting and Ranging

Explanation:
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9 817
Q:

If a carrier wave of 1000 kHz is used to carry the signal, the length of transmitting antenna will be equal to _____ ?

A) 300 m B) 30 m
C) 3 m D) 0.3 m
 
Answer & Explanation Answer: A) 300 m

Explanation:

h =  straight c over straight v = 3 × 108/106 = 300 m

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9 650
Q:

Quality of transmission depends upon

A) Nature of signal only B) Nature of medium only
C) Both (A) and (B) D) Neither A nor B
 
Answer & Explanation Answer: C) Both (A) and (B)

Explanation:

Quality of transmission is governed both by nature of signal and nature of communication channel/medium.

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7 613
Q:

The rate of change of linear momentum of a body falling freely under gravity is equal to it's ____ ?

A) Kinetic Energy B) Weight
C) Potential Energy D) Impulse
 
Answer & Explanation Answer: B) Weight

Explanation:

Rate of change of impulse equals the force . In case of freely falling body the only force is the weight.

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9 757
Q:

A disk and a sphere of same radius but different masses roll on two inclined planes of the same altitude and length. Which one of the two objects gets to the bottom of the plane first ?

A) Depends on their masses B) Sphere
C) Disk D) Both reach at the same time
 
Answer & Explanation Answer: B) Sphere

Explanation:

Time does not depend on mass, else

  => is least for 'sphere' and

hence least time is taken by sphere.

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6 694