Question

A $20kg$ body is pushed with just enough force to start it moving across a floor and the same force continues to act afterwards. The coefficient of static and kinetic friction are $0.6$ & $0.2$ respectively. The acceleration of the body is :

• A. $6m/s^2$
• B. $1m/s^2$
• C. $2m/s^2$
• D. $4m/s^2$

Answer 1

The correct option is D $4m/s^2$

The force needed to start the motion is nothing but static friction which is $\mu mg$ so the force applied is $\mu mg$ ;$\mu =0.6$ so force is $0.6mg$

Now once the body comes in motion the friction changes to kinetic so friction now is $0.2mg$ and it will oppose the motion.

So net force on the body will be $\text{Applied Force-Kinetic friction}=0.6mg-0.2mg=0.4mg$

So acceleration will be $NetForce/mass=0.4mg/m=0.4g=0.4\times 10=4m/s^2$

Option D is correct.