Question

17.
Two bodies A and B are thrown simultaneously. A is projected vertically upwards with 20 m/s speed
from the ground and B is projected vertically downwards from a height of 40 m with the same speed
and along the same line of motion. At what point do the 2 bodies collide? (g=9.8m/s?)​

Answer 1

Answer:

Explanation:

Suppose they meet at height 'h' from the ground in time 't'.

Initial velocity of projection be u=20 m/s

For the ball thrown upward (u and a are opposite)

h=ut−  

2

1

​  

gt  

2

.............(i)

For the ball thrown vertically downward (u and a are in same direction)

40−h=ut+  

2

1

​  

gt  

2

........(ii)

Add (i) and (ii) we get,

40=2ut

t=  

2u

40

​  

=  

2×20

40

​  

=1sec

Putting values in equation (i) we get,

h=20×1−  

2

1

​  

×9.8×1  

2

 

h=20−4.9

h=15.1m

Balls will collide at height 15m from the ground in 1sec