9th Class Science Force and laws of motion Question Bank MCQs - Force and Laws of Motion

A bus of mass 500 kg is moving with a velocity of 5 m/s and is acted upon by a forward force of 500 N due to engine and retarding force of 200 N due to friction. Velocity of bus after 20 s will be

A) 15 m/s

B) 17 m/s

C) 19 m/s

D) 21 m/s

Correct Answer: B

Solution :

[b] Given, m = 500 kg, u = 5 m/s and t = 20 s

Resultant force, F = 500 - 200 = 300 N

\[\therefore \]Acceleration, \[a\frac{F}{m}=\frac{300}{500}=0.6\ \operatorname{m}/{{s}^{2}}\]

By equation of motion,

v = u + at = 5 + 0.6 \[\times \] 20 =17 m/s