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Hailstones falling vertically with a speed of 10 m s^-1, hit the wind screen (wind screen makes an angle 30^@ with the horizontal) of a moving car and rebound elastically. Find the velocity of the car if the driver finds the hailstones rebound vertically after striking. .

Answer» <html><body><p><br/></p>Solution :For the driver to observe, the hailstones move vertically <a href="https://interviewquestions.tuteehub.com/tag/upward-721781" style="font-weight:bold;" target="_blank" title="Click to know more about UPWARD">UPWARD</a> after the <a href="https://interviewquestions.tuteehub.com/tag/elastic-967540" style="font-weight:bold;" target="_blank" title="Click to know more about ELASTIC">ELASTIC</a> collision. <br/> Let the velocity of hailstone w.r.t. car be `vec v_(h,c)` <br/> Then `vec v_h = vec v_(h,c) + vec v_c` <br/> `(vec v_h)_x = (vec v_(h,c) + vec v_c)_x` <br/> `vec v_h = vec v_(h,c) + vec v_c` <br/> `(vec v_h)_x = (vec v_(h,c) + vec v_c)_x` <br/> But `(vec v_h)_x = 0`, since hailstones fall vertically down. <br/> `rArr (vec v_h)_x = -(v cos 30^@) rArr |vec v_c|_x = |vec v_(h,c)|_x` <br/> Now, `(vec v_h)_y = (vec v_(h,c) + vec v_c)_y` <br/> Since `(v_h)_y = -10 ms^-1 , (v_c)_y = 0 rArr -10 = -V sin 30^@ + 0` <br/> `V sin 30^@ = 10 rArr V = <a href="https://interviewquestions.tuteehub.com/tag/20-287209" style="font-weight:bold;" target="_blank" title="Click to know more about 20">20</a> ms^-1` <br/> `(vec v_c)_x = V cos 30^@ = 20 xx (<a href="https://interviewquestions.tuteehub.com/tag/sqrt-1223129" style="font-weight:bold;" target="_blank" title="Click to know more about SQRT">SQRT</a>(<a href="https://interviewquestions.tuteehub.com/tag/3-301577" style="font-weight:bold;" target="_blank" title="Click to know more about 3">3</a>))/(2) = 10 sqrt(3) ms^-1` <br/> `vec v_c = 10 sqrt(3) ms^-1`. <br/> <img src="https://d10lpgp6xz60nq.cloudfront.net/physics_images/BMS_V01_C05_E01_070_S01.png" width="80%"/> , <img src="https://d10lpgp6xz60nq.cloudfront.net/physics_images/BMS_V01_C05_E01_070_S02.png" width="80%"/>.</body></html>


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