Physics Test 20

Result

Physics Test 20

Score
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Rank
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Weekly Quiz Competition

Question 1
4 / -1

A sound wave of wavelength λ travels towards the right horizontally with a velocity V. It strikes and reflects from a vertical plane surface, travelling at a speed v towards the left. The number of positive crests striking during a time interval of three seconds on the wall is

A
3 (V + v) /λ

B
3 (V – v)/λ

C
(V + v)/ 3λ

D
(V – v) /3λ

Solution

The relative velocity of sound waves with respect to the walls is V + v. Hence the apparent frequency of the waves striking the surface of the wall is (V + v)/ λ. The number of positive crests striking per second is the same as frequency. In three seconds the number is [3 (V + v)]/ λ.
Question 2
4 / -1

An athlete’s coach told his team that muscle times speed equals power. What dimensions does he view for “muscle”?

A
MLT²

B
ML²T^-2

C
MLT^–2

D
L

Solution

Power = force × velocity = muscle times speed
∴ muscle represents force
muscle = [MLT^-2]