Saved Bookmarks
| 1. |
A ball is thrown vertically upwards from the ground It crosses a point at the height of `25 m` twice at an interval of `4 secs`. The ball was thrown with the velocity of.A. `20m//sec`.B. `25m//sec`.C. `30m//sec`.D. `35m//sec`. |
|
Answer» Correct Answer - C Let `u` be velocity of ball with which it is thrown. `rArru(6)+(1)/(2)a(6)^(2)=420` `rArr u+3a=70` ....`(ii)` `h=ut+(-(1)/(2)g t^(2))25=ut-5t^(2)` `5t^(2)-ut+25=0` Let `t_(1),t_(2)` be its roots `t_(1)+t_(2)=u//5,t_(1)t_(2)=5` Given, `t_(2)-t_(1)=4sec`. `(t_(2)-t_(1))^(2)=16` `rArr(t_(2)+t_(1))^(2)-4t_(1)t_(2)=16` `((u)/(5))^(2)-4xx5=16u=30m//sec.` |
|