Question

Two balls are thrown simultaneously a vertically upward with a speed 50 M per second from the ground and vertically downward from a height of 100 metre with the same speed and along the same line at what point the balls collide also sketch the velocity time graph for the motion same scale

Answer 1

Given : 

Case 1:

For the ball A :

initialSpeed=u=20m/s[upwards]=-20m/s

a=10m/s²[downwards]=+10m/s²

time=t=tsec

Distance=Sa meters

From seond equation of motion,

Sa=ut+1/2at²

Sa=-20t+1/2x10xt²

Sa=-20t+5t² --------------equation(1)

Case II:

For ball B:

Initial speed=u=20m/s[downwards]=+20m/s

a=10m/s²[downwards]=+10m/s²

time =t sec

Distance =Sb meters.=(40-sa)

From seond equation of motion,

Sb=ut+1/2at²(4-Sa)

=20t+5t² ====[equation2]

Therefore , from equation 1 and 2 we get:

40=-20t+5t²+20t+5t²40

=10t²4=t²

t=2sec

Let us find out distance Sa in 2 sec

Sa=ut+1/2at²

sa=-40+20=-20m

From the ground that is at 20m the two balls will collide.