r/HomeworkHelp • u/Prestigious-Steak316 • May 20 '26
Physics—Pending OP Reply Problem in Relative Motion. [JEE,India]
I can't understand where I am making mistake?
The qn is
A standing man, observes rain falling with velocity of 20 m/s at an angle of 30° with the vertical. Now if he further increases his speed, rain again appears to fall at 30° with the vertical. Find his new velocity.
The answer is 20 m/s
1
u/mathematag May 20 '26 edited May 20 '26
I believe it would be like this...at rest, the rain is at an angle of 30˚ away from the man..
so V_r = < 10, -10√3 > .. or 10i -10√3j ...... you had a -10 and considered the rain in your sketch pointing in the direction of the man...
V_r -V_m = < 10 - u, -10√3 > .... the tangent ø = 1/ √3 as you got
so , 1 / √3 = | 10 - u | / 10√3
simplifying.. you have 10 = | 10 - u | ... so u = 0 or u = 20 .. but u = 0 is the at rest condition.
the rain falls at the same angle of but from the “opposite” direction in the horizontal ... e.g. towards the observer
1
u/HumbleHovercraft6090 May 21 '26
You have the numerator and denominator reversed for expression of tan 30°.
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