Question

A force of $80N$ is applied to a block of mass $40kg$ moving in a straight line across a horizontal floor. Find out the acceleration of the box if the kinetic friction acting on the box has a magnitude of $60N$ ?

• A. $0.25m/s^2$
• B. $0.5m/s^2$
• C. $1.0m/s^2$
• D. $2.0m/s^2$
• E. $3.5m/s^2$

Answer 1

The correct option is B $0.5m/s^2$

Let a be the acceleration of the box.

The equation of motion of the box, $ma=F-f$ (as friction force always opposite to applied force)

or $40a=80-60$

or $a=20/40=0.5m/s^2$