Question

A body travels $200cm$ in the first two seconds with cosntant speed and $220cm$ in the next $4$ seconds with constant deceleration. The speed of the body at the end of the $7^{th}$ second is

• A. $22.5cm/s$
• B. $12.5cm/s$
• C. $57.5cm/s$
• D. $0cm/s$

Answer 1

Answer: (C)

$57.5cm/s$

Let the initial velocity of the body be $U$.

In the first $2$ seconds, $200=2U⟹U=100cm/s$
In the next $4$ seconds, $220=4U-\frac{1}{2}16a=4U-8a=4\left(100\right)-8a\to a=22.5cm/s^2$

Velocity of the body at the end of $7^{th}$ second is $V=U-at=100-\left(22.5\right)\left(7\right)=-57.5cm/s$