First slide
Instantaneous acceleration
Question

Two balls of the same mass are shot upwards one after another at an interval of 2 seconds, along the same vertical line with the same initial velocity of 39.2 m/s. They will collide at a height :

Easy
Solution

When they collide displacement will be same but time of travel is t and t - 2.
h=Ut12gt2=U(t2)12g(t2)2
Solving t = 5 sec.
Substituting h = 73.5 m.

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