Question

18. A ball thrown up vertically returns to the thrower after 6 s.
Find
(a) the velocity with which it was thrown up.
(b) the maximum height it reaches, and
(c) its position after 4 s.
​

Answer 1

Explanation:

The ball takes a total of 6 s for its upward and downward journey. Hence, it has taken 3 s to attain the maximum height. Hence, the ball was thrown upwards with a velocity of 29.4 m s−1

Answer 2

Answer:

Explanation:

The ball returns to the ground after 6 seconds.

Thus the time taken by the ball to reach to the maximum height (h) is 3 seconds i.e t=3 s

Let the velocity with which it is thrown up be  u

(a). For upward motion,                

v=u+at

∴     0=u+(−10)×3                  

⟹u=30  m/s      

(b). The maximum height reached by the ball

h=ut+  1 /2 at2

h=30×3+  1/2 (−10)×3  2

               

h=45 m  

(c). After 3 second, it starts to fall down.  

Let the distance by which it fall in 1 s   be   d

d=0+  1/2 at  2 ′        

where   t  =1 s

′

d=  1/2×10×(1)  2

=5 m  

∴ Its height above the ground, h  

′

=45−5=40 m  

Hence after 4 s, the ball is at a height of 40 m above the ground.