Normal Reaction

Q.

A force of 5 N acts on a body of weight 9.8 N. What is the acceleration produced in $m/se{c}^2$

1. 49.00

2. 5.00

3. 1.46

4. 0.51

Q.

Calculate the force required to lift an object of mass $10\mathrm{kg}$.

Q. A block of mass of $10kg$ is in contact with the inner wall of a hollow cylindrical drum of radius $1m.$ The coefficient of friction between the block and the inner wall of the cylinder is $0.1.$ The minimum angular velocity needed for the cylinder to keep the block stationary when the cylinder is vertical and rotating about its axis, will be $\left(g=10m/s^2\right)$

1. $\sqrt{10}\frac{rad}{s}$
2. $\frac{10}{2\pi }\frac{rad}{s}$
3. $10\frac{rad}{s}$
4. $10\pi \frac{rad}{s}$

Q.

Using a horizontal force of $200\mathrm{N}$, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?

Q.

Name two types of forces?

Q.

An object is subjected to a force in the north-east direction. To balance this force, a second force should be applied in the direction

1. North-East

2. South

3. South-West

4. West

Q. Consider a body of mass $1.0kg$ at rest at the origin at time $t=0$. A force $\overrightarrow{F}=(\alpha t\hat{i}+\beta \hat{j})$ is applied on the body, where $\alpha =1.0N{s}^{-1}$ and $\beta =1.0N$. The torque acting on the body about the origin at time $t=1.0s$ is $\overrightarrow{\tau }$. Which of the following statements is (are) true?

1. $\left(\overrightarrow{\tau }\right|=\frac{1}{3}Nm$
2. The torque $\overrightarrow{\tau }$ is in the direction of the unit vector $+\hat{k}$
3. The velocity of the body at $t=1s$ is $\overrightarrow{v}=\frac{1}{2}(\hat{i}+2\hat{j})m{s}^{-1}$
4. The magnitude of displacement of the body at $t=1s$ is $\frac{1}{6}m$

Q.

Name the type of force which acts in the following cases:

1. A coolie lifts a luggage
2. A bicycle comes to rest slowly when the cyclist stops pedaling
3. A stone falls from a roof
4. A comb rubbed with silk attracts bits of paper
5. A string hangs with a load
6. A horse moves a cart
7. A magnet attracts an iron pin
8. A boy opens a door
9. An apple falls from a tree
10. A man rows a boat

Q.

A person (40 kg) is managing to be at rest between two vertical walls by pressingone wall A by his hands and feet and the other wall B by his back (figure 6-E11). Assume that the frictioncoefficient between his body and the walls is 0.8 and that limiting friction acts at all the contacts. (a) show that the person pushes the two walls with equal force. (b) Find the normal force exerted by either wall on the person. Take $g=10m/s^2$

Q.

At a place where the acceleration due to gravity is $10m{s}^{-2}$ a force of $5kg-wt$ acts on a body of mass $10kg$ initially at rest. Find the velocity of the body after $4$ second.

Q. A block of mass $m$ is kept on the floor of a freely falling lift. During the free fall of the lift, the block is pulled horizontally with a force of $F=5\text{N},{\mu }_s=0.1$. The frictional force on the block will be

1. $5\text{N}$
2. $2\text{N}$
3. $\text{Zero}$
4. $10\text{N}$

Q. The normal reaction between the blocks $N_1,N_2$ are

1. $50N,20N$
2. $100N,50N$
3. $50N,200N$
4. $100N,20N$

Q. A small collar of mass $m=100\text{g}$ slides over the surface of a horizontal circular rod of radius $R=0.3\text{m}$. The coefficient of friction between the rod and the collar is $\mu =0.8$. When the speed of the collar is $V=2{\text{ms}}^{-1}$, the resultant force on rod is

1. $\frac{\sqrt{31}}{3}N$
2. $\frac{\sqrt{21}}{3}N$
3. $\frac{\sqrt{51}}{3}N$
4. $\frac{\sqrt{41}}{3}N$

Q. A block $Q$ of mass $M$ is placed on a horizontal frctionless surface $AB$ and a body $P$ of mass $m$ is released on its frictionless slope. As $P$ slides by a length $L$ on this slope of inclination $\theta$, the block $Q$ would slide by a distance

1. $\frac{m}{M}L\cos \theta$
2. $\frac{m}{M+m}L$
3. $\frac{M+m}{mL\cos \theta }$
4. $\frac{mL\cos \theta }{m+M}$

Q. A body in SHM has time period $T_1$ seconds under influence of one force and the same body executes SHM with period $T_2$ seconds under the influence of another force. Find the time period (in s) of the same body when both forces act simultaneously in the same direction.

1. 
2. 
3. 
4. 

Q.

Suppose you are standing with your friend. Suddenly, you push your friend and he falls down. According to Newtons law third law, the friend has also pushed you with a force of equal magnitude. Why did you not fall down?

Q.

A rocket burns 0.4 kg of fuel per second and ejects out gas with a velocity of 8 km s^-1. Calculate the force exerted by the ejected gas on the rocket.

Q. Find acceleration of block $\text{B}$ if $F=40\text{N}$.
(Take $g=10{\text{m/s}}^2$)

1. $3{\text{m/s}}^2$
2. $0$
3. $5{\text{m/s}}^2$
4. $6{\text{m/s}}^2$

Q.

A person has mass 60 kg. The area under feet of the person is $180c{m}^2$. Find the pressure exerted on the ground by the person. [Take $g=10m{s}^{-2}$].

Q. Block is pushed from bottom of inclined plane with speed 6 m/s as shown in figure, find time after which the block will return to the initial position?

1. t=3.6s
2. t=12.8 s
3. t=4.2 s
4. Block will not return

Q. Block A is pressed against the wall by Force F, F=60 N, find friction force between block & wall. (${\mu }_s=0.8,{\mu }_k=0.7$)

1. 48 N
2. 42 N
3. 40 N
4. 36 N

Q. Blocks are at rest & pulled by F & F, find tension force in the string

1. T=0 N
2. T=13 N
3. T=23 N
4. T=18 N

Q. Find the tension T in the given diagram below.

Limiting friction between blocks and surface are also given in the figure.

1. 30 N
2. 20 N
3. 40 N
4. 50 N

Q. Two forces which are perpendicular to each other, act on a body. The resultant force $F_1$ makes an angle of ${60}^o$ with one force. The magnitude of the other force is?

1. $\sqrt{3}F/2$
2. $F/\sqrt{2}$
3. $F/2$
4. $2F$

Q. Lift can move along both $y-$axis and $x-$axis. A ball of mass $m$ is attached to the ceiling of lift with inextensible light rope and box of mass $m$ is placed against a wall as shown in the figure. Neglect friction everywhere. $N$ is the net force acting on $‘m^{\prime }$.
Match the statements in List $1$ with results in List $2$

$\begin{array}{cc}\text{List 1}& \text{List 2}\\ \text{A) In the figure, lift starts moving along x -axis then value of T may be}& \text{p) Zero}\\ \text{B) Lift starts moving toward right along x -axis, then value of N may be}& \text{q)}>mg\\ \text{C) Lift starts moving in upward direction (y -axis) then the value of T may be}& \text{r)}<mg\\ \text{D) Lift starts moving in downward direction, then value of T may be}& \text{s)}=mg\end{array}$

1. $A–q,s,B–q,r,s,C–q,r,D–p,r,s$
2. $A–q,s,B–q,r,s,C–q,s,D–p,r,s$
3. $A–p,B–q,s,C–r,s,D–p,r,s$
4. $A–p,s,B–p,r,s,C–q,s,D–p,r,s$

Q. When a body is placed on a table top, it exerts a force equal to its weight downwards on the table top but does not move or fall.
$\left(i\right)$ Name the force exerted by the table top.
$\left(ii\right)$ What is the direction of the force?

Q. A horizontal force of $10N$ is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and the wall is $0.2$. Find out the weight of the block.

1. $100N$
2. $2N$
3. $20N$
4. $50N$

Q. The force between a hollow sphere and a point mass at P inside it as shown in figure:

1. is attractive and constant
2. is attractive and depends on the position of the point with respect to center C
3. is zero
4. is repulsive and constant

Q.

State the action and reaction forces in the following

(i) moving rocket

Q. A block of mass 0.2 kg is held against a vertical wall by applying a horizontal force of 10 N (normal to wall) on the block. If the coefficient of friction between the block and the wall is 0.6, the magnitude of the frictional force acting on the block is (g = 10 m/s²)

0.2 kg द्रव्यमान के एक गुटके पर 10 N का क्षैतिज बल (दीवार के लम्बवत्) आरोपित कर इसे ऊर्ध्वाधर दीवार पर रखा जाता है। यदि गुटके तथा दीवार के मध्य घर्षण गुणांक 0.6 है, तब गुटके पर क्रियाशील घर्षण बल का परिमाण है

1. 6 N
2. 4 N
3. 5 N
4. 2 N