Physics
When two similar sources vibrate with slightly different frequencies, a regular rise and fall occurs in the loudness of tone. This phenomenon is known as

Resonance
Echo
Doppler effect
Beats

ANSWER DOWNLOAD EXAMIANS APP

Physics
It is easier to roll a barrel full of coal tar than to pull it because

the rolling friction is much less than the sliding friction
coal tar is a liquid and it flows in the barrel when it is rolled
more surface area of the barrel is in contact with the road when it is pulled
the full weight of the barrel comes into play when it is pulled

ANSWER DOWNLOAD EXAMIANS APP

Physics
Stars twinkle because

the intensity of light emitted by them changes with time.
the refractive index of the different layers of the earth's atmosphere ch
the distance of the stars from the earth changes with time.
None of these

ANSWER DOWNLOAD EXAMIANS APP