Latest Wipro Aptitude Question SOLUTION: After striking the floor , a rubber ball rebounds to 4/5th of the height from which it has fallen. Find the total distance that it travels before coming to rest if it has been gent

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After striking the floor , a rubber ball rebounds to 4/5th of the height from which it has fallen. Find the total distance that it travels before coming to rest if it has been gently dropped from a height of 120 m.

1-540m.
2-960m.
3-1080m.
4-1020m

Asked In Wipro Pranav Bharti (9 years ago)

Unsolved Read Solution (9)

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Read Solution (9) :

niroshkumar   (9 years ago)

{a/1-l}=={120/1-4/5+96/1-4/5}==1080

Is this solution Helpfull? Yes (9) | No   

Sachin Grover  (9 years ago)

the first drop is 120 m.After this the ball will rise by 96m and then again fall by 96 m.This process will continue in the form of infinite G.P with starting term as 120 and common ratio of 4/5 i.e. 0.8.
So using a/(1-r)={120/(1-0.8) + 96/(1-0.8)}

Is this solution Helpfull? Yes (5) | No   

bojanapu prashanthi  (8 years ago)

After the drop, it travels down for h meters and rebounds back to 4h/5 and travels down 4h/5 and rebounds back 4/5(4h/5) etc...

The total distance it travels = h + 4h/5+ 4h/5+ 4/5(4h/5)+ 4/5(4h/5) + 4/5*4/5(4h/5)+...

S= h + 2*4h/5 + 2(4/5)(4h/5) + ....

= h + 2{4h/5 + 4/5(4h/5) + ....}

= h + 2(Sum of infinite GP with initial term 4h/5 and common ratio 4/5)

Formula: Sum of Infinite GP with initial term ‘a’ and common ratio ‘r’ is a/(1-r)

S = h + 2{(4h/5)/(1-4/5)}

= h + 8h = 9h = 9*120 = 1080

Note: two things required to solve this problem are,

first- deciding how much distances it travels before and after each rebound

second- formula for infinite GP.

Is this solution Helpfull? Yes (2) | No   

kumari priyanka  (8 years ago)

the ans will be 1080m

Is this solution Helpfull? Yes (1) | No (1)  

shaik shafiq  (9 years ago)

can any one explain it

Is this solution Helpfull? Yes | No (1)  

Abhishek Kumar  (8 years ago)

120+ 196/(1-4/5)= 1080m

Here GP formed is 196, 153.6,.....
a=196
r=153.6/196=4/5
so the sum of n terms of GP is
s=a/(1-r)
120 is added.

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Mayank Singh  (8 years ago)

120+2*120*(4/5(1+(4/5)+(4/5)^2+(4/5)^3+.......))
=120+2*120*(4/5)*(1/(1-(4/5)))
=120+2*120*4
=1080

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malleswari  (8 years ago)

can any one explain

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Gundla tejaswini  (3 years ago)

{120/1-4/5+90/1-4/5}=1080

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