A block of mass m is in contact with the cart C as shown. The coefficient of static friction between the block and cart is $\mu$. The acceleration $\alpha$ of the cart that will prevent the block from falling satisfies

Question

 

$$(a)\;\alpha > mg/\mu \quad (b)\; \alpha >g/\mu\; m \quad (c)\; \alpha < g/ \mu \quad (d)\;\alpha \geq g/\mu$$