Question

A body covers $100cm$ in first $2$ second and $128cm$ in next four seconds moving with constant acceleration. Find the velocity of the body at the end of $8$ sec?

• A. 10 cm/sec
• B. 25 cm/sec
• C. 8 cm/sec
• D. 15 cm/sec

Answer 1

Answer: (C)

The distance in first two seconds
$s_1=u{t}_1+\frac{1}{2}a{t}_1^2$
$100=2u+\frac{a}{2}4\dots \dots .(1)$
$200=4u+4a$
The distance in $6$ seconds
$s_1+s_2=6u+\frac{a}{2}36$
$2\left(s_1+s_2\right)=12u+36\dots \dots (2)$
$2(228)=12u+36$
From equation $1$ and $2$ We get
$a=-6cm/se{c}^2$
$100=2u-\frac{6}{2}\times 4$
$2u=112V=u+at$
$v=56-6\times 8=8cm/sec$