How long does a ball take to fall from a roof to the ground 7 m below?

1 Answer
Oliver S.
May 7, 2018

See below

Explanation:

If we assume that there is no air resistance and the only force acting on the ball is that of gravity, we can use the equation of motion:

#s=ut+(1/2)at^(2)#

#s#=distance travelled
#u#=initial velocity (0)
#t#=time to travel given distance
#a#=acceleration, in this case #a=g#,the acceleration of free fall which is #9.81 ms^-2#

Hence:
#7=0t + (1/2)9.81t^2#

#7=0+4.905t^2#

#7/(4.905)=t^2#

#t approx 1.195 s#

So it takes barely a second for the ball to hit the ground from that height.

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