Elitmus
Exam
Numerical Ability
Complex Numbers
A basket ball is dropped from a height of 20 feet.It bounces back each time to a height which is one half of hthe height of the last bounce. How far approximately will the ball have travelled before it comes to rest?
A. 30 feet
B. 40 feet
C. 60 feet
D. Can not be determined
Read Solution (Total 8)
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- C. 60 feet
assume that ball will come to rest at infinity
distance covered = 20 + 10 + 10 + 5 + 5 + 2.5 + 2.5 + 1.25 + 1.25 + ...
= 20 + 2 *(10 + 5 + 2.5 + 1.25 + ....)
= 20 + 2 * 10/(1 - 1/2) [sum of infinite GP = a/(1-r)]
= 20 + 40
= 60 feet.
- 10 years agoHelpfull: Yes(22) No(0)
- total distance covered will be 60 feet appx..distance covered in each bounce will be twice the height of that bounce.
20ft + 2*10ft(rebounce)+ 2*5ft(rebounce)+2*2.5(rebounce)+2*1.25(rebounce)+...==60ft - 10 years agoHelpfull: Yes(5) No(0)
- sorry i had taken height as 10
for 20 20*2*2-20
60 - 10 years agoHelpfull: Yes(1) No(0)
- here r=1/2
therefore we kmow a/(1-r) for infinite g p series it is used so dor 1st and 2nd bounce we have
(20/(1-1/2))+10/(1-1/2)=60feet ans
- 10 years agoHelpfull: Yes(1) No(0)
- here we cannot determine the the distance travelled becoz it wont come to rest it will always bounce half,that means suppose after nth bounce the distance is 0.0001 micro feet. so in next bounce i.e n+1 bounce it will bounce 0.0001/2 micro feet..
- 10 years agoHelpfull: Yes(0) No(5)
- 10+2*10*1/2+2*10*(1/2)^2...........
2*(10*1/2+10*1/2^2.....)-10=2*10/(1-1/2)-10
20*2-10=30 - 10 years agoHelpfull: Yes(0) No(2)
- 60, as 20+10+10+5+5+2.5+2.5+1.25+1.25+0.625+0.625+..=60ft
- 10 years agoHelpfull: Yes(0) No(0)
- Distance covered = 20 + 10 + 10 + 5 + 5 + 2.5 + 2.5 + 1.25 + 1.25 + ...
It is a GP and we use sum of infinite no. formula = a(1/1-r)
a=20 r=1/2
= 20 + 20(1/1-(1/2))
= 20 + 40 [sum of infinite GP = a/(1-r)]
= 60 feet. - 2 years agoHelpfull: Yes(0) No(0)
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