Two balls of equal masses are thrown upwards along the same vertical direction at an interval of 2
s,with the same initial velocity of 39.2 m/s. The two balls will collide at a height of
(a) 39.2 m (b) 73.5 m
(c) 78.4 m (d) 117.6 m

Question

Two balls of equal masses are thrown upwards along the same vertical direction at an interval of 2
s,with the same initial velocity of 39.2 m/s. The two balls will collide at a height of
(a) 39.2 m (b) 73.5 m
(c) 78.4 m (d) 117.6 m

irishboy123 · Answer

the masses don't matter! more importantly, do you know the basic equations of motion?? here you can use $ x_1(t) = ut - \frac{1}{2} g t^2$ for the second ball, you'd need to subby in the time delay so $ x_2(t) = u(t-2) - \frac{1}{2} g (t-2)^2$ then solve out $x_1 = x_2$. https://en.wikipedia.org/wiki/Equations_of_motion

anonymous · Answer

Thank you for answering, yes i know eqns of motion but did not know how to apply them here. The answer given is (b)73.5 , but still not able to solve it.  Can you please explain in a detailed manner.

irishboy123 · Answer

yes, that seems right solving the equations for t: https://www.wolframalpha.com/input/?i=39.2*(t-2)+-+0.5+(9.81)+(t-2)%5E2++%3D+39.2*+t+-+0.5+(9.81)+(t)%5E2 finding the height: https://www.wolframalpha.com/input/?i=39.2*5+-+0.5+(9.81)+(5)%5E2