Work, power & energy Questions and Answers

Michael Jackson is pulling an object 6 0 m on a ground by using a string that is inclined with the horizontal The string sustains a tensile force of 42 N and the work done by the force applied by Mr Jackson is 240 J If Mr Jackson wants to know the angle of inclination of the string what would it be 20 degrees 28 degrees 30 degrees 18 degrees

The loss of kinetic energy The loss of kinetic energ due to the first impact mv 1 m ev mv 1 e m 2gh 1 e mgh 1 e

ration 14 In a ballistics demonstration a police officer fires a bullet of mass 50 0 g with a speed of 200 m s on soft plywood of thickness 2 00 cm The bullet emerges with only 10 of its initial kinetic energy What is the emergent speed of the bullet

A small block of mass m held compressed against a spring as shown in the figure The spring has force constant of k such that mg k 3m After releasing the block it collides a spheres of same mass which is suspended from a massless rod of length 3m The rod can freely rotated in a vertical circle about its top point Considering the coefficient of restitution 0 5 find the minimum compression in the spring so that sphere can complete full circle l m m k mmmmm

A compass needle free to turn in a horizontal plane is placed at the centre of a circular coil of 30 turns and radius 12 cm The coil is in a vertical plane making an angle of 45 with the magnetic meridian The needle points west to east when the current in the coil is 0 35 A The horizontal component of the earth s magnetic field in T at that location is A 3 9 x 10 5 Correct Answer 3 9 10 6 5 x 10 5 10

60 A ball of radius r rolls inside a hemispherical shell of radius R It is released from rest from point A as shown in figure The angular velocity of centre of the ball in position B about the centre of the shell is A

In the figure shown rod AB is light and rigid while rod CD is also rigid and hinged at midpoint O Rod can rotate without friction about O The time period of small oscillation of rod CD is T 2 Where m is mass of rod CD and k is spring constant of each spring The value of n is m nk A k eeeeeeeeee C heeeeeeeeee k reeeeeeeeeer k B O

B 1 An advertisement claims that a certain 1200kg car can accelerate from rest to a speed of 25 m s in a time of 8s What average power must the motor produce to cause this accoloration 2 1 Int

A55 kg man holds a weight of 20 kg on his head W is the work done by him against gravity if he moves distance of 20 m i on a horizontal road ii on Encline of 1 in 5 Take g 10 m s2

Two identical block each of mass M 9 kg are placed on a rough horizontal surface of frictional coefficient 0 1 The two blocks are joined by a light spring and block B is in contact with a vertical fixed wall as shown in figure A bullet of mass m 1 kg and vo 10 m s hits block A and gets embedded in it a Find the maximum compression of spring 0 m olink Mmmm b Find the minimum value of vo for which block B will just start moving left wards Spring constant 240 N m g 10 m s

a 5 If work W is done is blowing a bubble of radius R from soap solution then the work done in blowing a bubble of radius 2R from the same solution is a W 2 b 2W c 4W d 2 W

A body moving at 2 m s can be stopped over a distance x If its kinetic energy is doubled how long go before coming to rest if the retarding force remains unchanged A x B 2x C 4x A block weighing 10 N t D 8x

Is defined 1 Only in conservative fields 2 As the negative of work done by conservative forces 3 As the negative of workdone by external forces when AK 0 4 All of these

50 In the above problem between the two fragments when their position vectors are perpendicular to each other is 1 40 m 2 20m 3 10m 4 5m 51 At a certain height a shell at rest explodes into two equal fragments One of the fragments receives a horizontal velocity u The time interval after which the velocity vectors will be inclined at 120 to each other is 3u 2u u u

A force F x i x 2 N acts on a particle which moves in the XY plane a 1m Find the work done by F as it moves the particle from A to C fig along each of the paths ABC ADC and AC YK a C D A a B X

A bullet losses 1 n of its velocity in passing through a plank What is the least number of plan to stop the bullet Assuming constant retardation A car moving along a straight highu with

The speed of a swimmer in still water is 20 m s The speed of river water is 10 m s and is flowing due east If he is standing on the south bank and wishes to cross the river along the shortest path the angle at which he should make his strokes w r t north is given by a 45 west c 0 b 30 west d 60 west NEET 2019

The acceleration due to gravity on a planet A is 9 times the acceleration due to gravity on planet B A man jumps to a height of 2 m on the surface of A What is the height of jump by the same person on the planet B 1 2 9 m 3 6 m 2 18 m 4 2 3 m

The displacement x of a body of mass 1 kg on smooth horizontal surface as a function of time t is given by 1 where x is in metres and t is in seconds Find the work done by the external agent for the first one 3 second X

A bullet moving with a uniform velocity v stops suddenly after hitting the target and the whole mass melts to m specific heat S initial temperature 25 C melting point 475 C and the latent heat L Then v is given by 1 mv 1 mL mS 475 25 J 2 mS 475 25 mL 3 mS 475 25 mL 4 mS 475 25 ml JE mv 2J mv mv

7 Two blocks are connected to an ideal spring of stiffness 200 N m At a certain and the instantaneous blocks are moving in opposite directions with speeds 4 ms and 6 ms is increasing is elongation of the spring is 10 cm The rate at which the spring energy 2 kx d 100 J s 0 000 TL ne two

0 75Gm R from the A missile is launched at an angle of 60 to the vertical with a velocity surface of the earth Neglecting air resistance find the maximum height reached by the missile from the surface of the earth me mass of the earth Re radius of the earth

A ball is thrown up with a certain velocity at angle 0 to the horizontal The kinetic energy KE of the ball varies with horizontal displacement x as 1 3 KE KE X 2 4 KE N KE t X X

23 A body is initially at rest It undergoes one dimensional motion with constant acceleration The power delivered to it at time t is proportional to 1 1 t2 O 3 n 2 t 4 2

A block slides along a track from one level to a higher level by moving through an intermediate valley as shown in figure The track is friction less until the block reaches the higher level Then there is friction force which stops the block at a distance d The block s initial speed v is 6 0 ms the height difference h is 1 1 m and the coefficient of kinetic friction is 0 60 The value of d is 0 60 0

30 Force acting on a particle moving along x axis is as shown in figure Find points of stable and unstable equilibrium A F B C E

A diatomic gas of moleculer weight 30 gm mole is filled in a container at 27 C It is moving at a velocity 100 m s If it is suddenly stopped the rise in temperature of gas is 1 60 R 6x104 2 4 600 R 6x10

The instantaneous angular position of a point on a given by the equation e 2 6 rad where t is in second The magnitude of angular velocity of the point when angular acceleration becomes zero O 2 rad s O 4 rad s O 3 rad s O 6 rad s

backhoe exerts a force on a 726 45 kg pile of dirt that is resting on the ground The dirt is lifted 7 62 m and

1 The unit of thermal conductivity is a Wm K 1 c Jm K 2015 b JmK d Wm K

A particle of mass 0 3 kg subject to a force F kx with k 15 N m What will be its initial acceleration if it is release from a point 20 cm away from the origin a 15 m s b 3 m s c 10 m s d 5 m s

D A particle of mass 100g is thrown vertically upwards with a speed of 5 m s The work done by the force of gravity during the time the particle goes up is a 0 5 J 1 25 J me the partic VIC b c 1 25 J 0 5 J d simple

1 A water pump lifts water from a level 10 m below the ground Water is pumped at a rate of 30 kg minute with negligible velocity Calculate the minimum horsepower the engine should have to do this na

A particle of mass m and charge q moves with a constant velocity v along the positive x direction It enters a region containing a uniform magnetic field B directed along the negative z direction extending from x a to x b The minimum value of v required so that the particle just enter the region x b is qvB m q b a B m qaB m C 0

6 A wire suspended vertically from one of its ends is stretched by attaching a weight of 500N to the lower end The weight stretches the wire by 2mm Then the elastic energy stored in the wire is A 0 25 joules B 10 joules C 1 joule D 0 5 joules

0 and 20 The curve between potential en distance r between atoms of a diatomic molecule is shown in figure If FA FB FC FD and Faro B forces of interaction between atoms of molecule corresponding to points shown on curve then U A 1 169in d B C E 1 Fp FB FAI 2 FB 0

The Young s modulus of a wire is numericall equal to the stress at which 1 Strain produced in the wire is unity 2 Length of wire gets doubled 3 Length increases by 100 4 All of these

A frictionless track ABCDE ends in a circular loop of radius R A body slides down the track from point A which is at a height h 5 cm Maximum value of R for the body to successfully complete the loop is B D

Water flows through a horizontal pipe of varying cross section at a rate of 0 5 m s1 The speed of water at a point where area of cross section is 500 cm i 10 ms 1 50 ms 1 2 ms1 O 5 ms

Explain the difference between work in Physics and work as done every day example If you push a cart inside a store are you doing any work Describe an real world application of impulse momentum theorem J F dt mv mv0

9 An object is attached to a horizontal spring and somewhere along its motion has a kinetic and potential energies of 19 4 Joules and 24 9 Joules respectively Given the maximum displacement of the spring of 2 72 m the spring constant N m is

A ball of mass m is dropped from height h on a light platform fixed at the top of vertical spring as shown in the figure The platform is depressed by a distance x What is the spring constant A C me 2mgh x 2mg h x 1000 KEN B 2mgh x D 2mg h x

Force acting on a particle moving in the x y plane is F y i x N x and Yare in metre As shown in Fig the particle moves from the origin O to point A 6m 6m The figure shows three paths OLA OMA and OA for the motion of the particle from O to A Y A 6 m 6 m A L Along which of the three paths is the work done maximum M OA OMA OLA X

One end of a block placed on a horizontal smooth surface is attached with a spring of force constant 100 N m Other end of the spring is attached with a wall as shown in figure Initially spring was in natural length Suddenly a constant horizontal force of 10N started acting on the block towards right and as a result the block started moving towards right The energy stored in the spring when the block stops for the first time is

A particle of mass 1kg is free to move along x axis under influence of a conservative force The potential energy function for the particle is U x 5x J If the total mechanical energy of the particle is zero Particle will remain between 5 m to 5 m 5 2 m to 5 2 m 2 m to 2 m Clear Resp

A particle is released from rest at origin It moves under influence of potential field U x 3x kinetic energy at x 2 is fog feen arren fagfaff af U x 3x i fx fr A 2 J B 1 J C 1 5 J D O J Your Answer

F 2x 3x 2 Choose correct option F 2x 3x 2 Hafa f A x 1 2 is position of stable equilibrium x 1 2fef B x 2 is position of stable equilibrium fref C x 1 2 is position of unstable equilibrium 3ff i x 1 2 D x 2 is position of neutral equilibrium fef Your Answer B

A uniform cylinder of mass m and length having area of cross section a is suspended lengthwise with the help of a massless spring of constant k The cylinder is half submerged in a liquid of density p A small push and release makes it vibrate with small amplitude The frequency of oscillation is kang A m apg 1 k apg

A body of mass 1 kg is moving in a vertical circular path of radius 1 m The difference in kinetic energy at lowest and highest position is g 10 m s 10 J 20 J 25 J O 30 J

A plate of mass M length b and breadth a is initially lying on horizontal floor with length parallel to floor and breadth perpendicular The work done to erect on its breadth is mg mg b a 2 mg Omg a a 21 b a 2