$A$ man balances himself in a horizontal position by pushing his hands and feet against two parallel walls. His centre of mass lies midway between the walls. The coefficients of friction at the walls are equal. Which of the following is not correct?

An object of mass $10 \,kg$ is projected from the ground with a speed of $40 \,m/s$ at an angle of $60^{\circ}$ with the horizontal. The rate of change of momentum of the object one second after projection in $SI$ units is ........ [Take $g = 9.8 \,m/s^2$]

Two bodies $A$ and $B$ of masses $5 \, kg$ and $10 \, kg$ in contact with each other rest on a table against a rigid wall. The coefficient of friction between the bodies and the table is $0.15$. $A$ force of $200 \, N$ is applied horizontally to $A$. What are $(a)$ the reaction of the partition $(b)$ the action-reaction forces between $A$ and $B$? What happens when the wall is removed? Does the answer to $(b)$ change,when the bodies are in motion? Ignore the difference between $\mu_{s}$ and $\mu_{k}$.

In the figure,two blocks are connected by a uniform strut attached to each block with frictionless pins. Block $A$ weighs $400 \, N$,block $B$ weighs $300 \, N$,and the strut $AB$ weighs $200 \, N$. If $\mu = 0.25$ under block $B$,determine the minimum coefficient of friction under block $A$ to prevent motion.

$STATEMENT-1$: It is easier to pull a heavy object than to push it on a level ground.
$STATEMENT-2$: The magnitude of frictional force depends on the nature of the two surfaces in contact.

$A$ balloon of mass $m$ is descending down with an acceleration $\frac{g}{2}$. How much mass should be removed from it so that it starts moving up with the same acceleration?