Numerical - Distance traveled by a ball dropped from a height

Q.  A ball dropped from a wall of height h travels a distance of 50 m in last two seconds before landing. What is the height of the wall from which the ball was dropped?
- Published on 21 Sep 15

a. 120.15 m
b. 127.37 m
c. 183.48 m
d. Insufficient data

ANSWER: 127.37 m

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    Discussion

  • Osaid Ahmad   -Posted on 20 Jan 21
    The question is incorrect. It mentions that the ball travels 50m in the last 2 seconds. However, the solution denotes it an unknown variable t. I think the solution doesnt match the question. the correct value should be 69.62m
  • Sravanthi   -Posted on 15 Dec 15
    Let H be the height of wall, time required to travel 50 m is t and till the ground is (t+1)
    Solution:

    S = ut + (½) gt2 1/2

    - (H – 50) = 0 – (½) x 9.81 t2

    H = 4.905 t2 + 502---------- (1)

    Without considering the distance traveled of 50 m, we get

    - H = 0 – (½) x 9.81 (t + 1)2

    H = 4.905 (t + 1)2 ---------- (2)

    From (1) and (2)

    4.905 t2 + 502 = 4.905 (t + 1)2

    t = 3.096

    Height of wall = 127.37 m

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