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# 7. A boy throws a table tennis ball of mass 20 g upwards with a velocity of u 0 = 10 m/s at an angle q 0 withthe vertical. The wind imparts a horizontal force of 0.08 N, so that the ball returns to the starting point.Then, the angle q 0 must be such that, tan q 0 is(A) 0.2 (B) 0.4 (C) 2.5 (D) 1.2

419 Points
10 years ago

Dear Deepak

see the pic for the solution

All the best.

AKASH GOYAL

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509 Points
10 years ago

for verticle motion

Uy = U0COS@   &   ay = -g

applying  VY = UY + ayt

Vy at topmost point is zero so

t= uy/g

tim of flight (T)= 2t=2Uy/g .........1

for horizontal motion

Ux = UOCOS@

Sx = UxT + axT2

finally particle reaches to same point so displacement  is zero ..

0 = UxT + axT2/2    .........2

putting value of T in eq 2

Uy/Ux = g/a  .........3

max = force =0.08

ax = 4m/s2

now , UY/UX = Uocos@/Uosin@

=tan@=10/4=2.5

option c is correct