IIT JEE , AIEEE Forum - Physics , Mechanics

mukulss

see the ans wer is C) ie 60 seconds......
see :
till acceleration becomes 0:
:

v = u + at

and when it is fired vertically up with a constant acceleration,
u = 0,

v = 10(30)m/s

that is when its fuel is emptied,
it obviously will attain speed of 300m/s

now due to inertia,
it will continue moving up 4 atime 't' till its velocity is 0 or say till attains a mx ht .
now our ans shall be:

t + 30 sec. bcoz it is asked frm the starting moment....

now to cal t:
v = u - gt
v = 0,
of course.....
t = 30 sec..

and hence the ans is 60 sec.....

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