Question

A body moving with uniform acceleration describes 12 m in the third second of its motion and 20 m in the 5th second. Find the velocity after 10 th second.

• A. 40 m/s
• B. 42 m/s
• C. 52 m/s
• D. 4m/s

Answer 1

Answer: (B)

$S_n=u+\frac{a}{2}(2n-1)$
$12=u+\frac{a}{2}(2\times 3-1)$ ..(i)
and $20=u+\frac{a}{2}(2\times 5-1)$ ..(ii)
Subtract Eq. (i) from Eq. (ii)
$8=\frac{a}{2}(9-5)=2a$
$\Rightarrow$ $a=4m/s^2$
From Eq. (i) $12=u+\frac{4}{2}\times 5$
$u=2m/s$
Velocity $v=u+at=2+4\times 10$
$=42m/s$