1
Q:

# A nuclear reactor is said to have become 'critical' when

 A) it stops due to malfunctioning B) it starts emitting dangerous radioactive radiations C) it is shut down to avoid explosion D) it is ready to produce controlled energy

Answer:   D) it is ready to produce controlled energy

Explanation:

To produce controlled energy i.e energy at a controlled or steady rate, the number of fissions per second must be controlled and maintained at that rate. Excess neutrons should be absorbed by control roads like cadmium.

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

Explanation:

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9 787
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 =   = 3 × 108/106 = 300 m

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9 635
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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6 592
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

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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8 728
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

Explanation:

Time does not depend on mass, else

$\inline \fn_jvn T \prec \sqrt{\left ( 1 +\frac{k^{2}}{R^{2}} \right )}$

$\inline \fn_jvn \frac{k^{2}}{R^{2}}$  => is least for 'sphere' and

hence least time is taken by sphere.