6for kid initial vel. = 0
a = 9.8 m/s^2
distance = 11.8 - 1.8 = 10
s = ut + 1/2 a t^2
find t = 1.42 s
in this time man has to reach the bottom of the building...
so vel. = 7 / 1.42 = 4.9
a healthy young man standing at a distance of 7m from a 11.8 m high building sees a kid slipping from the top floor . with what speed (assumed uniform ) should he run to catch the kid at an arm height (1.8m)
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7 Answers
1yes, i try to solve the problems which is mentioned above,but i am unable to find the solution of it.
1Assume the taken to reach to the foot of the tower by man be t secs. and speed be v.
v*t=7 ...... (1)
For the boy....
11.8-1.8=0+1/2*gt2 ....... (2)
Squaring (1).... and dividing by (2)
v2/g=49/10
Therefore....
[g=10m/s2]
v2=49
v=7 [ reqd. velocity of man ]
1Assume that the time taken to reach the foot of the tower by the man be t secs. and speed be v.
v*t=7 ....... (1)
For the boy......
11.8-1.8=0+1/2*gt2 ....... (2)
Squaring (1) ..... and dividing by (2)
2*v2/g=49/10
Therefore...
[g=10 m/s2]
v2=49/2
v=7/√2 m/s
v=3.9 m/s (approx.) is the reqd. answer.
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49general appeal to "TARGET" IITANS: Do 1 thing for these type of questions...instead of giving the solution...give hints to the question and let the one having difficulty in the question figure out the solution himself/herself...that would help him/her more...
for example for this question the obvious hint would have been::
"Time taken by man to reach the building must be equal to the time taken for the boy to reach the arm height...the man can take less time than this but not more!!!"
49a question to Amit Kumar...a continuation to this question!!
1) Assuming the man moves with double the minimum speed required to save the child, how long he has to wait after reaching the building's base before catching the falling child?
2) Assuming the man moves with double the minimum speed required, what will be the trajectory of the falling boy as seen by the man from the time he starts running and he catches the boy?? (if possible draw a rough diagram!!)
3) If the man had run with half the required speed, he unfortunately would have failed to save the boy...so find the trajectory of the boy as seen by the man assuming that he continues to run till he reaches the building's base!! Give trajectory for the time from which the man starts running till the time he reaches the buildings base!!