1
Q:

# Hot water is poured simultaneously in four metallic tumblers painted outside with different points. After some time the water will be found to have cooled most in the tumbler painted.

 A) rough white B) rough black C) shining white D) shining black

Answer:   B) rough black

Explanation:

Black  surfaces are good emitters of heat ( They are also good absorbers of heat). If the black surface is rough too, the emitting will be better. So (b) is the correct answer. Shining surfaces reflect back radiation. So if the black surface is also shining the effectiveness of emitting heat is lessened.

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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9 799
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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9 642
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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6 602
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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8 738
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

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

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

hence least time is taken by sphere.

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6 684