Two blocks of masses m and 2 m are placed one over the other as shown in figure.The coefficient of friction between m and 2m is `mu` and between 2m and ground is `(mu)/(3)`. If a horizontal force F is applied on upper block and T is tension developed in string, then choose the incorrect alternative.

Options

A. If F=`(mu)/(3)`mg, T=0
B. If F=`mumg`, T=0
C. If F`=2mu mg,T=(mumg)/(3)`
D. If F=`3mu mg, T=0`

Answer

C

Explanation

( c) `f_(1)`= maximum value of friction between m and 2m`=mu mg`
`f_(2)`= maximum value of friction between 2m and ground `=(mu)/(3)(3m)g=mu mg`
Now, let us draw free body diagram of m and 2m in all four cases.


Note Tension will be zero in all four cases.