Question

The speed of a body is doubled when it moves over a distance of $10m$. If the initial speed be $u$, what will be the speed after further coverage of distance $10m$?

• A. $\sqrt{5}u$
• B. $\sqrt{6}u$
• C. $\sqrt{7}u$
• D. $\sqrt{8}u$

Answer 1

The correct option is C $\sqrt{7}u$

If the acceleration be $a$ then using the third equation of motion, $v^2=u^2+2as$

we have $(2u{)}^2=u^2+2a\times 10$ so $a=3u^2/20$....(1)

After further covering 10 m taking initial speed at the $moment$ it has covered the $first$ $10m$ as $2u$ we get $v^2=(2u{)}^2+2a\times 10$ , putting value of $a$ from equation-1 we get $v^2=\sqrt{7}u$

Option C is correct.