Question

Find the time after which the two balls will collide.

• A. $4s$
• B. $5s$
• C. $6s$
• D. $8s$

Answer 1

The correct option is A $4s$

$\Rightarrow$ motion of ball B relative to A is uniform motion.

${\overrightarrow{v}}_{BA}={\overrightarrow{v}}_B-{\overrightarrow{v}}_A=+30-(-20)=50\text{m/s}$


$\Rightarrow \overrightarrow{s}={\overrightarrow{v}}_{AB}\times t+\frac{1}{2}{\overrightarrow{a}}_{AB}{t}^2\Rightarrow 200=50\times t\Rightarrow t=4s$