Q. A stone is dropped from the window of a bus moving at 60 km/hr. If the window is 196cm high, what is the distance along the track which the stone moves before striking the ground ?

1 Answer
Steve J.
Jun 15, 2018

Let's get our units consistent.
Acceleration due to gravity: #g = 9.8 m/s^2#
Speed: #60 cancel(km)/cancel(hr) * (1000 m)/(1 cancel (km)) * (1 cancel(hr))/(3600 s) = 16.67 m/s#
Distance to fall: #196 cancel(cm) * (1 m)/(100 cancel(cm)) = 1.96 m#

We need the time to hit the ground, so we need the formula

#y = u*t + 1/2*a*t^2#

#1.96 m = 0 + 1/2*9.8 m/s^2*t^2#

#t^2 = (2*1.96 cancel(m))/(9.8 cancel(m)/s^2) = 0.4 s^2#

#t = 0.632 s#

Now we can calculate the distance down the road it travels in that time. It is

#d = 16.67 m/cancel(s) * 0.632 cancel(s) = 10.5 m#

I hope this helps,
Steve

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