Force

Q. The force exerted by the floor of an elevator on the foot of a person standing there is more than the weight of the person if the elevator is -

$\left(a\right)$ Going up and slowing down
$\left(b\right)$ Going up and speeding up
$\left(c\right)$ Going down and slowing down
$\left(d\right)$ Going down and speeding up

1. $a,b$
2. $a,c$
3. $b,c$
4. $b,d$

Q. A conductor $PQ$ carrying a current $i$ is placed perpendicular to a long conductor $XY$ carrying a current $I$. The direction of force on $PQ$ will be

1. Towards left
2. Towards
3. Upwards
4. Downwards

Q. Two army persons A and B each of weight $500\text{N}$ climbs up a rope through a height of 10 m. A takes 20 sec, while B takes 40 sec to achieve this task. What is the ratio of powers of person A and B?

1. $\text{1:2}$
2. $\text{1:4}$
3. $\text{2:1}$
4. $\text{14:1}$

Q. Find the conversion factor SI unit of force and CGS unit of force ?

Q. Tension in a string is i) Gravitational force ii) Electromagnetic force iii) Strong nuclear force iv) Weak nuclear force

Q. The speed of the block when it reaches the point $Q$ is

1. $10\sqrt{3}m{s}^{-1}$
2. $20m{s}^{-1}$
3. $10m{s}^{-1}$
4. $5m{s}^{-1}$

Q. Consider a planet moving in an elliptical orbit around the Sun. The work done on the planet by the gravitational force of the Sun.

1. Is zero in any small part of the orbit
2. Is zero in some parts of the orbit
3. Is zero in complete revolution
4. Is zero in no part of the motion

Q. A 1 m metallic rod is rotated with an angular velocity of 400 rad/s about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant and uniform magnetic field of 0.5T parallel to axis exists everywhere. Derive the expression of emf developed between the centre of the ring and also calculate its value.

Q. When you roll a ball on the ground, it comes to rest after moving some distance. The ball comes to stop because -

1. You did not hit the ball hard enough.
2. There is a force on ball supporting the motion.
3. There is a force on ball opposing the motion.
4. None of these

Q. An open knife edge of mass $m$ is dropped from a height $h$ on a wooden floor. If the blade penetrates up to the depth $d$ into the wood, the average resistance offered by the wood to the knife edge is

1. $mg$
2. $mg(1+\frac{h}{d})$
3. $mg{(1+\frac{h}{d})}^2$
4. $mg(1-\frac{h}{d})$

Q. Which one of the following is measured by the area between the balancing line and themass-haul curve ?

1. Haul between the balancing points
2. Earthwork accumulated up to that point
3. Excess of excavation
4. Excess of filling

Q. Given figure shows a man with a parachute. Name the force which is responsible for his downward motion. Will he come down with the same speed without the parachute?

1. Force of gravity, No
2. Air resistance, No
3. Air resistance, Yes
4. Force of gravity, Yes

Q. A uniform chain of length $\text{L}$ and mass $\text{M}$ is lying on a smooth table and one third of its length is hanging vertically down over the edge of the table. If $\text{g}$ is acceleration due to gravity, the work required to pull the hanging part on the table is

1. $\text{MgL}$
2. $\frac{MgL}{3}$
3. $\frac{MgL}{9}$
4. $\frac{MgL}{18}$

Q. State two effects of a force when applied on a body.

Q. A slab consists of two parallel layers of two different materials of same thickness having thermal conductivities $K_1$ and $K_2$. The equivalent thermal conductivity of the slab is :

1. $\frac{K_1+K_2}{K_1{K}_2}$
2. $\frac{2K_1{K}_2}{K_1+K_2}$
3. $\frac{K_1+K_2}{2}$
4. $K_1+K_2$

Q. an electron is moving vertically downwards at any place . the horizontal component of earths magnetic field acts upon it .what will be the direction of magnetic force acting on the electron

Q. If a body is at rest on an inclined plane, how many forces are acting on it amd name the forces.

Q. A bead of mass m = 0.2 kg lies at a distance r from the axis of rotation on a rigid wire as shown in figure. Coefficient of friction between wire and bead is $\mu$, and wire starts rotating from rest at an angular acceleration of $\alpha$ at t = 0. The whole arrangement is in gravity free region. r = 1m, $\mu =0.4$ & $\alpha =0.1r/s^2$

1. Relative motion between bead and wire starts at t = 2 sec
2. Power of friction force at t = 2 is 0.0016 watt
3. Power of normal contact at t = 2 is 0.004 watt
4. Power of net force on bead at t = 2 is 0.004 watt

Q.

A wall consists of alternating blocks with length d and coefficient of thermal conductivity. The cross-sectional area of the blocks is the same. The equivalent coefficient of thermal conductivity of the wall between left and right is

1. $K_1+K_2$
2. $\frac{\left(K_1+K_2\right)}{2}$
3. $\frac{K_1{K}_2}{K_1+K_2}$
4. $\frac{2K_1{K}_2}{K_1+K_2}$

Q. 52.What is static cling?

Q. An ideal spring with spring constant $k$ is hung from the ceiling and a block of mass $M$ is attached to its lower end. The mass is released with the spring initially unstretched. Then the maximum extension in the spring is (Given acceleration due to gravity $=g$)

1. $\frac{2Mg}{k}$
2. $\frac{Mg}{k}$
3. $\frac{Mg}{2k}$
4. $\frac{4Mg}{k}$

Q. If a force $10N$ is applied on a spring the extension produced is ................ if spring constant $=2.62N/m$

1. $6.2m$
2. $3.8m$
3. $4m$
4. $2m$

Q. A uniform chain of length $\text{L}$ and mass $\text{M}$ is lying on a smooth table and one third of its length is hanging vertically down over the edge of the table. If $\text{g}$ is acceleration due to gravity, the work required to pull the hanging part on the table is

1. $\frac{MgL}{3}$
2. $\frac{MgL}{9}$
3. $\frac{MgL}{18}$
4. $\text{MgL}$

Q. $A,B$ and $C$ are the three forces each of magnitude $4N$ acting in the plane of paper as shown in Fig. The point $O$ lies in the same plane. Name the forces producing anticlockwise moments.

1. $A$
2. $B$
3. $C$
4. both A & B

Q. A cord is used to lower vertically a block of mass $M$ by a distance $d$ with constant downward acceleration $g/4$. Work done by the cord on the block is:

1. $Mg\frac{d}{4}$
2. $3Mg\frac{d}{4}$
3. $-3Mg\frac{d}{4}$
4. $Mgd$

Q. Newton is the unit of which quantity.

1. Acceleration
2. Force
3. Mass
4. Gravity

Q. two weights w1 and w2 are tied to the ends of a string passing over a frictionless Pulley when the pulley is move upwards with an acceleration g the tension in the string is

Q. An open knife edge of mass '$M$' is dropped from height '$h$' on a wooden floor. If the knife penetrates upto depth '$d$' into the wood, the average resistance offered by the wood to the knife edge is

1. $mg$
2. $mg(1-\frac{h}{d})$
3. $mg(1+\frac{h}{d})$
4. $mg{(1+\frac{h}{d})}^2$

Q. A uniform chain of mass m and length l is suspended vertically. The lower end of the chain is lifted up to the point of suspension. The work done by the gravitational force is?

1. $\frac{mgl}{4}$
2. $\frac{mgl}{2}$
3. $\frac{mgl}{3}$
4. mgl

Q. Under the influence of which set of forces among the options below can a body not be in equilibrium?

1. $(3\text{N},4\text{N},8\text{N})$
2. $(3\text{N},1\text{N},2\text{N})$
3. $(3\text{N},4\text{N},5\text{N})$
4. $(3\text{N},4\text{N},7\text{N})$