Question

The velocity of a ball $v$ is thrown vertically upwards is represented by the equation $v=5t^2+20t-60$ where $v$ represents velocity and $t$ represent time in seconds. Calculate the time when the ball stops for the first time.

• A. $2$
• B. $3$
• C. $6$
• D. $12$

Answer 1

The correct option is A $2$

A state of rest is defined as $v=0$. Hence $5t^2+20t-60=0$ or $t^2+4t-12=0$ or $(t+6)(t-2)=0$ or $t=-6,2$. But $t=-6$ is not possible. Hence $t=2sec$.