Two rings are suspended from the points A and B on the ceiling of a room with the help of strings of length 1.2 m each as shown. The points A and B are separated from each other by a distance AB = 1.2 m. A boy standing on the floor throws a small ball so that it passes through the two rings whose diameter is slightly greater than the ball. At the moment when the boy throws the ball, his hand is at a height of 1.0 m above the floor. A stop watch which is switched on at the moment of throwing the ball reads 0.2 s when the ball passes through the first ring and 0.6 s when it passes through the second ring.

The projection speed of the ball is:

Options

A. 4.3 m
B. 3.2 m
C. 2.8 m
D. 2.5 m

Answer

C

Explanation

Horizontal separation between the rings 1.2 m. is 1.2 m. Time spent from 1st ring to 2nd ring= 0.4 sec.
Let y is the vertical separation between the hand of the boy and the ring `rArr y=u_(y) (0.2) -10/2 (0.2)^(2) and y=u_(y) (0.6) -10/2 (0.6)^(2) rArr u_(y)=4m//s and y=0.6 m`
height of the room =1+0.6+1.2=2.8m