CBSE Questions for Class 11 Engineering Physics Work,Energy And Power Quiz 9 - MCQExams.com

A bod of mass M is suspended by a massless string of length L.The horizontal velocity V at position A is just sufficient to make real the point B.The angle $$\theta$$ at which the speed of the bob is half of that it A satisfies:
1270979_917d575b5ec54ed1b84b2a7ffa04ba11.png
  • $$\theta=\dfrac{\pi}{4}$$
  • $$\dfrac{\pi}{4} < \theta<\frac{\pi}{2}$$
  • $$\dfrac{\pi}{2} < \theta<\dfrac{3\pi}{4}$$
  • $$\dfrac{3\pi}{4} < \theta<\pi$$
A body of mass 1 kg begins to move under the action of a time dependent  force $$ \overrightarrow { F } =(2t\hat { i } +3t^{ 2 }\hat { j } ) $$ N, where $$ \hat { i } $$ and $$ \hat { j }  $$ are unit vectors along x and y axes. What power will be developed by the force at the time t?
  • $$ (2t^2+3t^2)W $$
  • $$ (2t^4+4t^4)W $$
  • $$ (2t^3+3t^4)W $$
  • $$ (2t^3+3t^5)W $$
Two wires of the same diameter of the same material having the length $$\ell$$ and $$2\ell$$. If the force is applied on each, the ratio of the work done in the two will be
  • $$1: 2$$
  • $$1: 4$$
  • $$2: 1$$
  • $$1: 1$$
By applying a force $$F=(3xy-5z) j +4zk$$ a particle is moved along the path $$y=x^2$$ from point $$(0,0,0)$$ to the point $$(2,4,0)$$. The work done by the F on the particle is (all values are in SI units)
1270771_88cb9d01112c47d38e7adb03c6428eff.png
  • $$\dfrac { 280 }{ 5 } J$$
  • $$\dfrac { 140 }{ 5 } J$$
  • $$\dfrac { 232 }{ 5 } J$$
  • $$\dfrac { 192 }{ 5 } J$$
Two masses $$10 \ gm$$ and $$40 \ gm$$ are moving with kinetic energies in the ratio $$9:25$$. The ratio of their linear momentum is:
  • $$5:6$$
  • $$3:10$$
  • $$6:5$$
  • $$10:3$$
A force is acting on a particle varies with the displacement x as $$F=ax-bx^2$$. Where a=1 N/m and $$b=1 N/m^2$$. The work done by this force for the first one meter (F is in newtons, x is in meters) is :
  • $$\dfrac{1}{6}J$$
  • $$\dfrac{2}{6}J$$
  • $$\dfrac{3}{6}J$$
  • None of these
The work done in placing a charge of 8$$\times $$$${ 10 }^{ -18 }$$ coulomb on a condenser of capacity 100 micro-farad is 
  • 16$$\times { 10 }^{ -32 }$$ joule
  • 3.2$$\times { 10 }^{ -26 }$$ joule
  • 4$$\times { 10 }^{ -10 }$$ joule
  • 32$$\times { 10 }^{ -32 }$$ joule
A particle of mass 1 kg is projected under gravity at an angle $${ 37 }^{ o }$$ with horizontal with 50 m/s. Instantaneous power delivered by gravity at t=1s is $$\left( sin{ 37 }^{ o }=\frac { 3 }{ 5 } ,cos{ 37 }^{ o }=\frac { 4 }{ 5 }  \right) $$
  • 200 J/s
  • -200 J/s
  • Zero
  • -400 J/s
Mass of $$B$$ is four times that of $$A . B$$ moves with a velocity half that of $$A$$. Then, $$B$$ has 
  • kinetic energy equal to that of $$A$$
  • half the kinetic energy of $$A$$
  • twice the kinetic energy of $$A$$
  • kinetic energy one-fourth of $$A$$
A particle is moving in a vertical circle. The tension in the string when passing through two positions at angles $${30}^{o}$$ and $${60}^{o}$$ from vertical (lowest position) are $${T}_{1}$$ and $${T}_{2}$$ respectively, then
  • $${T}_{1}={T}_{2}$$
  • $${T}_{2}> {T}_{1}$$
  • $${T}_{1}> {T}_{2}$$
  • tension in the string always remains the same
A body of mass $$2\ kg$$ moving under a force has relation between displacement $$x$$ and time $$t$$ as $$x=\dfrac{t^{3}}{3}$$ where $$x$$ is in metre and $$t$$ is in sec. The work done by the body in first two second will be
  • $$1.6\ joule$$
  • $$16\ joule$$
  • $$160\ joule$$
  • $$1600\ joule$$
Work done by a force $$\vec{F}=(\hat{i}+2\hat{j}+3\hat{k})\ N$$ action on a particle in displacing it from the point $$\vec{r}_{1}=\hat{i}+\hat{j}+\hat{k}$$ to the point $$\vec{r}_{1}=\hat{i}-\hat{j}-2\hat{k}$$
  • $$-1\ J$$
  • $$2\ J$$
  • $$-13\ J$$
  • $$zero$$
A particle moves along positive X-axis from x=$$0$$ to x=$$5$$ under influence of force is given by$$F={ x }^{ 2 }-2x-8.$$ The work done by the force is 
  • -69 units
  • -23.33 units
  • -5 units
  • zero
The displacement (x) and time (t) for a particle are related as $$t=\sqrt { x } +3$$. What is the work done in the first six second of its motion?
  • 3 J
  • 4 J
  • Zero
  • 5 J
Five identical balls each of mass m and radius r are strung like beads at random and at rest along a smooth, rigid horizontal thin rod of length L, mounted between immovable supports. Assume $$10r<L$$ and that the collision between balls or between balls and supports are elastic. If one ball is struck horizontally so as to acquire a speed v, the average force felt by the support is 
1299290_d7b92577c587474fa13923eeaaeb0893.PNG
  • $$\dfrac { 5m }{ L-5r } $$
  • $$\dfrac { m{ v }^{ 2 } }{ L-10r } $$
  • $$\dfrac { 5m{ v }^{ 2 } }{ L-10r } $$
  • $$\dfrac { m{ v }^{ 2 } }{ L-5r } $$
When a 4 kg mass is hung vertically on a light spring obey's Hooks law , the spring stretches by 2 cms. The work required to be done by an external agent in stretching this spring by 5 cm will be ( g =9.8 $${ ms }^{ -2 }$$ )
  • 4.9 J
  • 2.4 J
  • 0.495 J
  • 0.24 J
A position dependent force $$F = 7 - 2x + 3x^2$$ newton acts on a small body of mass $$2 kg$$ and displaces it from $$x = 0$$ to $$x = 5$$. The work done in joule is :
  • $$70$$
  • $$270$$
  • $$35$$
  • $$135$$
Two bodies of masses $$4kg$$ and $$16kg$$ are at rest. The ratio of times for which the same force must act on them to produce the same kinetic energy in both of them is
  • $$1:4$$
  • $$2:1$$
  • $$1:2$$
  • $$4:1$$
$$\overrightarrow { F }  =x\hat i+y\hat j$$, is this force:
  • a conservation force
  • a non conservation
  • depends upon X
  • depends upon $$y \quad \& \quad x$$
 A force of $$1200 \mathrm { N }$$ acting on a stone by means of a rope slides the stone through a distance{ of$$ 10 \mathrm { m }$$in a direction inclined at $$ 60 ^ { \circ } $$ force. The work done by the force is
  • $$6000 \sqrt { 3 } J$$
  • 6000 J
  • 12000 J
  • 8000 J
$$\begin{array} { l } { \text { A man weighing } 80 \mathrm { kg } \text { climbs a staircase } } \\ { \text { carrying a } 20 \mathrm { kg } \text { load. The staircase has } 40 } \\ { \text { steps, each of } 25 \mathrm { cm } \text { height. If he takes } 20 } \\ { \text { seconds to climb, the work done is } } \end{array}$$
  • $$9800 \mathrm { J }$$
  • $$245 \mathrm { J }$$
  • $$98 \times 10 ^ { 4 } J$$
  • 7840 J
The tension in the string revolving in a vertical circle with a mass m at the end which is at the lowest position  
  • $$\dfrac{mv^2}{r}$$
  • $$\dfrac{mv^2}{r}-mg$$
  • $$\dfrac{mv^2}{r}+mg$$
  • $$mg$$

The work done by a force $$F=(-6x^3\hat
i)$$ in displacing a particle from $$x = 4m$$ to $$x = -2m$$ is:     
  • $$- 240$$ J
  • $$360$$ J
  • $$420$$J
  • will depend upon the path
A variable force given by $$ F= ( 3x^2 \hat i + 4 \hat j) $$ acts on a particle. the force is in newton and x is in meter. what is the change in KE of particle as it moves from point (2, 3) to (3, 0) 
  • -7J
  • zero
  • 7J
  • 19J
Work done by air when it expands from 50 litres to 150 litres at a constant pressure of 2 atmospheres is:
  • $$2\times { 10 }^{ 4 }J$$
  • $$2\times { 10 }0J$$
  • $$2\times { 10 }^{ 5 }\times 100J$$
  • $$2\times { 10 }.5\times 100J$$
does not vary from point to point in space Which pair of the following forces will never give resultant force of 2 N?
  • 1 N and 3 N
  • 2 N and 2 N
  • 1 N and 1 N
  • 1 N and 4 N
A force $$F_1$$ on a body of 2 kg produces an acceleration of $$2.5 m/m^2$$ and other force $$F_2$$ acting on another body of mass 5 kg produces an acceleration of $$2 m/s^2$$. The ratio of $$F_2/F_1$$ is
  • $$2$$
  • $$4$$
  • $$6$$
  • $$8$$
A hollow smooth uniform sphere $$A$$ of mass $$m$$ rolls without sliding on a smooth horizontal surface. It collides elastically and head-on with another stationary smooth hollow sphere $$B$$ of the same mass mm and same radius. The ratio of the kinetic energy of $$B$$ to that of $$A$$ just after the collision is 
1361865_11e6976e511a4024abd91ae2aaca3faf.PNG
  • $$1 : 1$$
  • $$2 : 3$$
  • $$3 : 2$$
  • $$\rm{None}$$
The speed of a motor increases from 1200 rpm to 1800 rpm in 20 s. How many revolutions does it make during these second?
  • 400
  • 600
  • 500
  • 700
If body of mass 2 kg is moving along X axis under an external force, whose displacement is given by $$x(t) = 3t^2 - 2t + 5 m$$. Find the work done by force from t = 0 to t = 5 sec.
  • $$78\quad J$$
  • $$780\quad J$$
  • $$840\quad J$$
  • $$200\quad J$$

AB is long frictionless horizontal surface. One end of an ideal spring of spring constant K is attached to a block of mass m, which is being moved left moved left with constant velocity v, and another end is free.Another block of mass 2m is given a velocity 3v towards the spring. Work done by an external agent in moving m with constant velocity v in a long time will be:
  • $$ - 5m{v^2}$$
  • $$ - 8m{v^2}$$
  • $$ - 3m{v^2}$$
  • None of these
A force $$\vec { F } = 2 x \hat { i } + 3 y ^ { 2 } \hat { j } \mathrm { N }$$ where x and y are in meter, acts upon a particle. Find work done (in J) by this force in displacing the particle from (1 m, 2 m, 5 m) to (2 m, 3 m, 2 m).
  • 24
  • 16
  • 28
  • 22
When a simple pendulum is rotated in a vertical plane with constant angular velocity, centripetal force is:
  • maximum at highest point
  • maximum at lowest point
  • same at all points
  • zero
In the figure, at the free end of the light string, a force $$F$$ is applied to keep the suspended mass of $$18 $$\mathrm { kg }$$ at rest. Assuming



1402949_aca715d872ac4b2caeb287507171715b.png
  • $$240 N$$
  • $$120 M$$
  • $$180 M$$
  • $$240 M$$
A block of mass 10 kg is moving up on an inclined plane with constant acceleration 2 m/sec by applying a constant force F as shown in the fig. The work done on the block by applied force F in 2 s is
1392596_8ea8b2aa4e354531ac6c0508ebcbd0e6.png
  • 480
  • 240
  • 960
  • none
A force $$\vec { F } =\left( { 3x }^{ 2 }+2x-7 \right) $$ N acts on a 2 kg body as a result of which the body gest displaced x=0 to x=5 cm. The work done by the force will be-
  • 35 Joule
  • 70 Joule
  • 115 Joule
  • 270 Joule
A particle moves along the x-axis from x=0 to x=5 m under the influence of a force given by $$F=\left( { 7-2x+3x }^{ 2 } \right) N.$$ The work done in the process is
  • 70 J
  • 270 J
  • 35 J
  • 135 J
The amount of work done in stretching a wire by 10N force can cause an elongation of $$2×{ 10 }^{ -2 }m$$ will be 
  • 10 J
  • 1 J
  • 0.1 J
  • 0.01
Velocity-time graph of a particle of mass 2 kg moving in a straight line is as shown in figure. Work done by all the forces on the particle during the motion is:
1392827_e49dbb3dfa6a4ecc918b83069c161981.JPG
  • $$400 J$$
  • $$-400 J$$
  • $$-200 J$$
  • $$200 J$$
A particle is displaced from a position $$(2\hat { i } -\hat { j } +\hat { k } )$$ metre to another position $$(3\hat { i } +2\hat { j } -2\hat { k } )$$ meter under the action of force $$(2\hat { i } +\hat { j } -\hat { k } )$$ N. Work done by the force is:
  • 8 J
  • 10 J
  • 12 J
  • 36 J
A cone filled with water is whirled in a vertical circle of radius 4 m. What will be the time period of rotation so that water does not fall ?
  • 4 s
  • 6 s
  • 2 s
  • 1 s
A balloon with its contents weighing 160 N is moving down with an acceleration of g/2 $${ ms }^{ -2 }$$ the mass to be removed from it so that the balloon moves up with an acceleration of g/3$${ ms }^{ -2 }$$ is 
  • 5 kg
  • 10 kg
  • 6 kg
  • 3 kg
In $$10 s$$, a body of $$6 kg$$ mass is dragged $$8 m$$ with uniform velocity across a floor by a steady force of $$20 N$$. The K.E of the body is:
  • $$2.92 J$$
  • $$0.92 J$$
  • $$1.92 J$$
  • $$0J$$
The breaking strength of a string is 55 kg wt. The maximum permissible speed of a stone of mass 5 kg which revolved in a vertical circle of radius 4 m with the help of is the string is g=10 $$ {s}^{2} $$.
  • $$

    10 \mathrm{m} / \mathrm{sec}

    $$
  • $$

    15 \mathrm{m} / \mathrm{sec}

    $$
  • $$

    20 \mathrm{m} / \mathrm{sec}

    $$
  • $$

    25 \mathrm{m} / \mathrm{sec}

    $$
A force of $$ \left(4 x^{2}+3 x\right)  $$ N acts on a particle which displaces it from $$  x=2 m  $$ to $$  x=3 \mathrm{m}  $$.
The work done by the force is
  • $$32.8 J$$
  • $$3.28 J$$
  • $$0.328 J$$
  • zero
A body of mass m is rotating in a vertical circle of radius 'r' with critical speed. The difference in its K.E. at the top and the bottom is _____.
  • 2mgr
  • 4 mgr
  • 6 mgr
  • 3 mgr
A spring of force constant $$800 N/m$$ has an extension of $$5 cm$$. The work done in extending it from $$5 cm$$ to $$15 cm$$ is :
  • $$16 J$$
  • $$8 J$$
  • $$32 J$$
  • $$24 J$$
Two springs of force constants $$  \mathrm{K}_{1}  $$ and $$  \mathrm{K}_{2}  $$ $$ \left(\mathrm{K}_{1}>\mathrm{K}_{2}\right)  $$ are stretched by same force. If $$  \mathrm{W}_{1}  $$ and $$  W_{2}  $$ be the work done stretching the springs then
  • $$

    W_{1}=W_{2}

    $$
  • $$W
    _1<W_2$$
  • $$

    \mathrm{W}_{1}>\mathrm{W}_{2}

    $$
  • $$

    W_{1}=W_{2}=0

    $$
A vertical spring of force constant $$100 N/m$$ is attached with a hanging mass of $$10 kg$$. Now an external force is applied on the same so that the spring is stretched by additional $$2m$$. The work done by the force is ($$g= 10 m/s^2$$)
1431733_656c2220f8e945e68795cc6f8812bf8c.png
  • $$200 J$$
  • $$400 J$$
  • $$450 J$$
  • $$600 J$$
At the instant speed of block is maximum, the magnitude of force exerted by spring on the block is
1433820_5df2a0e6894142068553c4a15c8a1b98.png
  • $$\dfrac{mg}{2}$$
  • $$mg$$
  • Zero
  • None of these
0:0:1


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