New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    A ball is dropped from a height of 120 metres. After each

    bounce, it rises to one-fourth of the height from which it fell. What is the total distance the ball travels before coming to rest?
    A 200 m Correct Answer Incorrect Answer
    B 180 m Correct Answer Incorrect Answer
    C 240 m Correct Answer Incorrect Answer
    D 220 m Correct Answer Incorrect Answer

    Solution

    Distance travelled in 1 st  fall = 120 m

    Height to which the ball will rebound in 1 st  fall = 120/4 = 30 metres

    Height to which the ball rebounds in 2 nd  fall = 30/4 = 7.5 metres

    Therefore, distance travelled by ball = 120 + 30 + 30 + 7.5 + 7.5……. upto infinity

    = 120 + 2 × (30 + 7.5 + up to infinity)

    = 120 + 2 × 30/{1 – (1/4)} [sum of infinite G.P. = a/(1 – r)]

    = 120 + 60 × 4/3 = 120 + 80 = 200 metres

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