Question

A body is allowed to fall from a height of hundred metres after 2 seconds if acceleration due to gravity vanishes the total time of its fall is

Answer 1

Answer:

time-6 seconds

Explanation:

first, for the 2 seconds, s=ut+1/2at^2

so displacement in first 2 seconds=20m, therefore 100-20=80m is left to travel. the body will travel with the same constant velocity as much it had at the end of 2 seconds. v=u+at,v=10x2 ,v=20m/s, the ball has to travel the rest 80m with velocity of 20m/s, so, v=s/t

20=80/t ,t=80/20= 4 seconds. so total time=4+2 seconds for which gravity did act in the body, t=6

Answer 2

Answer:

ans 60

Explanation:

distance travelled in 2 seconds is y=1/2gt^2=1/2×10×4=20m

velocity required after 2 seconds is V =gt=10×2=20ms

As there is no acceleration, that body would travel the remaining distance (100-20=80m) with uniform velocity of 20ms

time taken for the remaining journey is 80/20= 4s

i.e total time of motion is 2+4 =6s