First slide

Friction

Question

A 3 kg block A is placed on the top of a 4 kg block B as shown. To make the block A slip on B, assuming frictionless table, a horizontal force of 9 N is to be applied to the top block. Find the minimum horizontal force (in N) that can be applied to lower block so that A slips on B.

Moderate

Solution

$f_{max} = 3 μ g$
When 3 kg and 4 kg blocks move together, common acceleration, $a = \frac{9}{4 + 3} = \frac{9}{7} m / s^{2}$
$\begin{array}{l} \begin{array}{l} For 4 k g block, f_{\max} = 4 a \\ \Rightarrow μ (3 g) = 4 \times \frac{9}{7} \end{array} \\ \Rightarrow μ = \frac{12}{7 \times 10} = \frac{6}{35} \end{array}$
If force F is applied common acceleration, $a = \frac{F}{7} m / s^{2}$
$\begin{array}{l} For 3 kg block f_{max} = 3 μ g = 3 \times a \\ \Rightarrow 3 (\frac{6}{35}) \times 10 = \frac{3 F}{7} \end{array}$
$\Rightarrow F = 12 N$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App