Question

3 children are pushing a block of mass M towards right with equal forces. Their father is also pushing the same block with a force of 45 N towards left as shown below:
Given the frictional force is 12 N and the block moves towards left, what can be the maximum force applied by each child?

• A. 10N
• B. 11N
• C. 33N
• D. 30N

Answer 1

The correct option is B 11N

Since the block moves towards left, the force applied by father is greater than or equal to the resultant of the force applied by children and the force of friction. Moreover, friction will act towards right.
Hence, $3x+12\le 45$
$\Rightarrow x\le \frac{33}{3}$
$\Rightarrow x\le 11N$