A block of mass $\mathrm{m}$ is in contact with the cart $\mathrm{C}$ as shown in the figure. The…

A block of mass $\mathrm{m}$ is in contact with the cart $\mathrm{C}$ as shown in the figure. The coefficient of static friction between the block and the cart is $\mu$. The acceleration $\alpha$ of the cart that will prevent the block from falling satisfies
  1. $\alpha > \frac{m g}{\mu}$
  2. $\alpha > \frac{g}{\mu \mathrm{m}}$
  3. $\alpha \geq \frac{g}{\mu}$
  4. $\alpha < \frac{g}{\mu}$

Solution

When a cart moves with some acceleration toward right then a pseudo force (ma) acts on block toward left. This force $(m \alpha)$ is action force by a block on cart Now, block will remain static w.r.t. cart, if frictional force $\mu \mathrm{R} \geq \mathrm{mg}$ $\begin{array}{crrr} \Rightarrow & \mu \mathrm{m} \alpha & \geq \mathrm{mg} & \text { [as } \mathrm{R}=\mathrm{m} \alpha \text { ] } \\ \Rightarrow & \alpha & \geq \frac{g}{\mu} & \end{array}$

Asked in: NEET 2010 (Screening)

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