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Physics: Post your doubts here!

hellodjfos;s'ff

hellodjfos;s'ff

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Mr."S" said:
How to solve this
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P=E/t, KE=1/2(m)(v^2), D=m/V
m=D*V
KE=1/2(D*V)(v^2)
The volume is broken up into area and length
P=1/2(D*A*l)(v^2)/t
l/t=v, so:
P=1/2(D*A*v^3)
This gives an input power of 1300kW. Since the efficiency is 50%, the output power is 650kW, hence the answer B.
 
hellodjfos;s'ff

hellodjfos;s'ff

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Kanekii said:
Why is Angle 35?
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Because they gave the angle between the two first order maximum. The angle in the equation dsin(theta)=n(lamda) is the angle between the central maxima and the order, so to get this angle you divide 70 by 2 which is 35.
 
hellodjfos;s'ff

hellodjfos;s'ff

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MShaheerUddin said:
View attachment 64117
Hellp ? :/
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When the source of wave is travelling at a higher speed, the observed frequency rises(you can test this using values and the formula), so A and B are ruled out. When a source of wave approaches an observer, the observed frequency increases. So, initially the observer was detecting a microwave with a higher frequency than the microwave's actual frequency. So, when the microwave emitter stops, the observed frequency falls below f0. So the answer is C.
 
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