NCERT Solutions for Chapter: Laws of Motion, Exercise 4: SA

 A mass of$2 \mathrm{kg}$ is suspended with thread $AB$ (figure). Thread $CD$ of the same type is attached to the other end of $2 \mathrm{kg}$ mass. Lower thread is pulled gradually, harder and harder in the downward direction so as to apply force on $AB$. Which of the threads will break and why?

In the above-given problem if the lower thread is pulled with a jerk, what happens? 

 Two masses of $5 \mathrm{kg}$ and $3 \mathrm{kg}$ are suspended with help of massless inextensible strings as shown in Figure. Calculate $T_1$ and $T_2$ when whole system is going upwards with acceleration $=2 \mathrm{m} {\mathrm{s}}^{-2} \left(\text{ use }\mathrm{g}=9.8 \mathrm{m} {\mathrm{s}}^{-2}\right)$

 Block $A$ of weight $100 \mathrm{N}$ rests on a frictionless inclined plane of slope angle $30°$(Figure). A flexible cord attached to$A$ passes over a frictionless pulley and is connected to block $B$ of weight $W$. Find the weight $W$ for which the system is in equilibrium.

A block of mass $M$ is held against a rough vertical wall by pressing it with a finger. If the coefficient of friction between the block and the wall is $\mu$ and the acceleration due to gravity is $g$, calculate the minimum force required to be applied by the finger to hold the block against the wall?

A $100 \mathrm{kg}$ gun fires a ball of 1kg horizontally from a cliff of height $500 \mathrm{m}$. It falls on the ground at a distance of $400 \mathrm{m}$ from the bottom of the cliff. Find the recoil velocity of the gun. (acceleration due to gravity$=10 \mathrm{m} {\mathrm{s}}^{-2}$)

Figure $\left(a\right)$ and $\left(b\right),$ shows $(x, t),(y, t)$diagram of a particle moving in $2$ dimensions If the particle has a mass of $500\mathrm{g}$, find the force (direction and magnitude) acting on the particle.

A person in an elevator accelerating upwards with an acceleration of $2 \mathrm{m} {\mathrm{s}}^{-1}$, tosses a coin vertically upwards with a speed of $20 \mathrm{m} {\mathrm{s}}^{-1}$. After how much time will the coin fall back into his hand? $\left(g=10 \mathrm{m} {\mathrm{s}}^{-2}\right)$