# Question #9e417

Mar 14, 2017

$6 s$

#### Explanation:

Using Newton's Second law of Motion
$F = m a$
Solving for acceleration and inserting given values we get
$a = \frac{F}{m}$
$\implies a = - \frac{50}{20} = - 2.5 m {s}^{-} 2$
$- v e$ sign indicates that it is a retarding force.

Now using the kinematic equation
$v = u + a t$
$0 = 15 - 2.5 t$
$\implies t = \frac{15}{2.5} = 6 s$