A block P of mass m is placed over a plank of mass M. Plank Q is placed over a smooth horizontal surface as shown in a given figure. Block P is given a velocity v to the right. If μ is the coefficient of friction between P and Q, the acceleration of Q relative to P is
1
μg
2
μmg/M
3
\(\mu g\left( {1 - \frac{m}{M}} \right)\)
4
\(\mu g\left( {1 + \frac{m}{M}} \right)\)