Work, power & energy Questions and Answers

Statement 1 When a glass container containing water at room temperature is kept over a flame the level of water first decreases slightly then increases Statement 2 On heating at room temperature 27 C water first contracts and then expands A Statement 1 is true statement 2 is true and statement 2 is correct explanation for statement 1 B Statement 1 is true statement 2 is true and statement 2 is NOT the correct explanation for statement 1 C Statement 1 is true statement 2 is false D Statement 1 is false statement 2 is true

C F 3yi 4x A particle is moving on x axis has potential energy U 2 20 X 5x Joules along x axis The particle in released at x 3 The maximum value of x will be x is in meters and U is in joules C 7 m D 8 m B 3 m A 5 m

A 2 2 kg block starts from rest on a rough inclined plane that makes an angle of 25 with the horizontal The coefficient of kinetic friction is 0 25 As the block goes 2 0 m down the plane the mechanical energy of the Earth block system changes by 1 Zero 3 9 8 J 5 18 J 2 9 8 J 4 18 J

A body of mass 2 kg is moving up an inclined plane rising 1 in 30 with velocity 60 m sec If efficiency is 40 then calculate power required

of mass m is connected by string of length L to point P The system is released from rest with the pendulum bob in a horizontal position Which of the following graph is correctly showing the variation of T tension with 8 P 1 T 3 T 90 90 0 0 2 T n 4 T 90 90 0 0

When work is done on a body by an external force its 1 Only kinetic energy increases 2 Only potential energy increases 3 Both kinetic and potential energies may increase 4 Sum of kinetic and potential energies remains constant

AB is an L shaped obstacle fixed on a horizontal smooth table A ball strikes it at A gets deflected and restrikes it at B If the velocity vector before collision is V and coefficient of restitution of each collision is e then the velocity of ball after its second collision at B is f ur Aq

The acceleration of block is 3m C 5g 8 8q Smooth 3m 2 A B 3g 2m

5 AC K e x xo li Take the value of potent FoXo 1 2e Which of the following is are CORRECT 2 The force on a particle is given by F x F e energy at x X as U x A there is one stable equilibrium B there is one unstable equilibrium C there is no neutral equilibrium D the graph of potential energy as a function of x is Xo U x X

d sin 8 cos 8 g 22 Two identical balls A and B are released from the positions shown in figure They collide elastically on horizontal position MN The ratio of the heights attained by A and B after collision will be neglect friction a 1 4 c 4 13 45 M 60 N b 2 1 d 2 5 h a Th ne b T c T d 26 A se cach The adja v to

CHOOSE THE ONE OR 11 A ball of mass 1kg is dropped from a height of 3 2m on smooth inclined plane The coeffici 1 of restitution for the collision is e 1 collision 2 The ball s velocity becomes horizontal after the 3 2m 0 The angle 0 tan 2 B The speed of the ball after the collision 4 2 m s C The total loss in kinetic energy during the collision is 8J D The ball hits the inclined plane again while travelling vertically downward

a spring through 4 A block of mass m moving with speed v compue of spring constant distance x before its speed is halved What is the nolutife 2 Insioitisno to 102 s nori irigied s2mot allst lsd Isonadg2 A 3mv A 3mv 291 of pain B mvd lader C vosonsteib D 2 2 2 4x s 4x 12 81 2 2x SMS

A force among many other forces is delivering power to a body of mass 1 kg at a rate of P 3t 4 Then change in kinetic energy of body is 2 s will be 1 Cannot be determined 2 Must be positive 3 Must be zero ho 154 joules

1 Spring is oscillating with frequency 4Hz having spring constant k An identical spring is connected in series in new system as shown in figure Find new frequency W k oooooo 1 2Hz 191 AIT m k k mmmmm 2 2 2Hz m

A block of mass m 2 kg is moving with velocity vo towards a massless unstretched spring of force constant k 10 N m Coefficient of friction between the block and the ground is 1 5 Find the maximum value of vo so that after pressing the spring the block does not return back but stops there permanently LALO B 12 m s Vo 8000 C 10 m s D None of these

A block of mass m is being pulled upon the roug inclined plane by a man delivering constant power P The coefficient of friction between the block and the inclined is u The maximum speed of block during ascent is 1 3 S zago 0 P mg sin0 cos 0 P no ULCOSA mysino P 2 2P mg sin 0 u cos 0 3P 4 mg sine cos 0

A block of mass 10 kg moving in x direction with a constant speed of 10 ms 1 is subjected to a retarding force F 0 1x J m during its travel from x 20 m to 30 m Its final KE will be AIPMT 2015 1 250 J 2 475 J 3 450 J 4 275 J

1 A small body of mass m is located in a horizonta plane at point O The body accelerates uniformly and acquires horizontal velocity u then mean power developed by the friction force during the whole time of motion if friction coefficient is k 3mu 1 4kg 5 2 mukg

A pendulum bob carries a positive charge q Another positive charge q is held at the point of support then the time period of bob is L length of the simple pendulum 1 Greater than 2 2 Less than 2 3 Equal to 2 I to 20 g 9 24 L g

A small bead of mass m can move on a smooth circular wire km radius R under the action of a force F directed r position r of bead from P K constant towards a point P within the circle R at a distance from the centre What should be the minimum 2 velocity in m s of bead at the point of the wire nearest the centre of force P so that bead will complete the circle K Take 8 unit 3R R 2 LL P

41 Shown in the figure if potential at point A is taken to be zero the potential at point Bis 2011M In the 1A R R of Hilt A a IV c 2V D iv 1A C 2A 2V tila mm www b 2V d 1V B A2A

An object shaped as L is placed between two parallel plane mirrors as shown In the first seven closest images how many laterally inverted images are formed 1 1 4 4 2 2 3 3

An open knife edge of mass M dropped from a height h on a wooden floor If knife penetrates distance s into the wood the average resistance offered by the wood to the knife is 1 Mg 3 Mg 1 2 2 Mg h S 4 Mg 1 h S

Which of the following statements is correct a Kinetic energy of a system can be changed without changing its momentum b Kinetic energy of a system cannot be changed without changing its momentum c Momentum of a system cannot be changed without changing its kinetic energy d A system cannot have energy without having momentum 15

A force F K y i x where K is a positive constant acts on a particle moving in the x y plane Starting from the origin the particle is taken along the positive x axis to the point a 0 and then parallel to the y axis to the pint a a The total work done by the force F on the particle is A 2Ka B 2Ka C Ka D Ka ulor noth shown below As it moves along the path its

A small bob of mass m is tied to a fixed point O by an inextensible string of length in the vertical plane as shown Initially the string is just taut 30 and it is released from rest Which of the following statement is correct A When the string again becomes taut it will break B When the string again becomes taut its momentum will be conserved perpendicular to the string C Work done by impulsive tension is mgl 4 D Work done by tension is zero

by a chine that 5 A particle of mass m is delivers a constant power k watts If the particle starts from rest the force on the particle at time AIPMT 2015 t is 1 mk 2 mk t2 12 mk V2 TIN t 3 mk t

8 Water is drawn from a well in a 5 kg drum of capacity 55 L by two ropes connected to the top of the drum The linear mass density of each rope is 0 5 kg m The work done in lifting water to the ground from the surface of water in the well 20 m below is g 10 ms 2 a 1 4 x 104 J b 1 5 x 104 J c 9 8 x 10 6 J d 18 J

A bomb of mass 10 kg explodes into two pieces of masses 4 kg and 6 kg If kinetic energy of 4 kg piece is 200 J Find out kinetic energy of 6 kg piece 400 1 J 3 100 3 J 2 4 200 3 300 J J

A open knife edge of mass M is dropped from a height h on a wooden floor If the blade penetrates a distance S into the wood average resistance offered by the wood to the blade is 1 Mg h 3 Mg 1 1 S 2 Mg 1 h S 4 Mg 1 5 S

A force F 31 21 4k displaces a body from a point A 8 2 3 to the point B 2 0 6 The work done is a 1 unit b 2 units c 3 units d 4 units

A force of 50 N is applied on block which makes an angle of 30 with the smooth horizontal surface as shown in figure below Calculate the work done in moving the block by 20 cm horizontally 3 50 N eizoludu 30 201A e asids d mmi to aquo owi eni amsh 0

TE TUITIONS XI 26 Three forces acting on a body are shown in the figure To have the resultant force only along the y direction the magnitude of the minimum additional force needed is a 3N AN b 0 5 N c 1 5 N d EN 30 60 2N IN Prof Parchure

B Which one of the following arrangements truly represent the property indicated against it A Br Cl F bond energy B Br Cl F2 electronegativity C Br Cl F oxidising power D Br Cl F electron affinity

5 Calculate the power of an engine which can maintain a speed of 50 m s for a train of mass 3 x 106 kg on a rough level track The coefficient of friction is 0 05 Given g 10 m s 2 7 5 x 104 kW

A uniform chain of length L and mass M is lying on a smooth table and one third of its length is hanging vertically down over the edge of the table If g is acceleration due to gravity the work required to pull the hanging part on the table is A MgL C MgL 2 B D MgL 3 MgL 18

3 A stone of mass 2 kg tie with the help of thread of length 2 m and moves in vertical circular motion The difference between tension in the thread at lowest point and at the highest point is Take g 10 m s NCERT Pg 122 1 60 N 2 120 N 3 30 N 4 240 N

38 The position time graph for a particle moving alon a straight line is shown in figure The total distan travelled by it in time t 0 to t 10 s is x m 10 1 Zero 3 20 m 2 leut t s 46 8 10 2 10 m 4 80 m 0

3 The mass of a bucket full of water is 13 kg It is being pulled up from a 10 m deep well Due to a hole in the bucket 4 kg water flows out of the bucket The work done in drawing the bucket out of the well will be g 10m s 1 900 J 3 1100 J 2 1300 J 4 1700 J

10 A uniform chain AB of mass m and length 1 is placed with one end A at the highest point of a hemisphere of radius R Referring to the top of the hemisphere as the datum level the potential energy of the chain is given TR that given that 2 Fig 8 234 B

A light spring of length 20 cm and force constant 2 N cm is placed vertically on a table A small block of mass 1 kg falls on it The length h from the surface of the table at which the ball will have the maximum velocity is A 20 cm ibrant Academy 1 22 Im B 15 cm 1411m C 10 cm D 5 cm

A smaller bar A resting on a smooth horizontal plane is attached by threads to a point P and by means of a weightless pulley to a weight B possessing the same mass as the bar itself Besides the bar is also attached to a point O by means of a light non deformed spring of 5mg length and stiffness k where m is the mass P A 10000 0000 10 10 B of bar The thread PA having been burned the bar starts moving Find its velocity at the moment when it breaking off the plane

3 m M 1 Zero F E 7 The bob mass m of a simple pendulum of length L is held horizontal and then released It collides elastically with a block of equal mass lying on a frictionless table The kinetic energy of the block after collision will be 2 mal N 3 2mgL 4 mgL

A particle moves on a rough horizontal ground with 3 some initial velocity say Vo If of its kinetic energy 4 is lost due to friction in time to then coefficient of friction between the particle and the ground is 3vo Vo Vo 1 2 3

A small block of mass 0 5 kg is projected speed of 2 m s on a horizontal smooth floor which merges into a rough horizontal circular ring in shape of a quarter circle and moves along its inside as shown in the figure The coefficient of friction between the block and circular path is 0 2 If the radius of the circular path is 2 m then the friction force acting on the block when it reaches end of circular path is the figure shows top view 1 0 456 N 7211 5 N 2 1 01 N 4 0 106 N

132 A stationary object explodes into masses m and m2 They move in opposite directions with velocities V and V The ratio of kinetic energy E to kinetic energy E2 is MH CET 2014 2 m d 2m m m b m m a m m c

1 A wire is stretched under a force If the wire suddenly snaps the temperature of the wire 1 Remains the same 2 Decreases 3 Increases 4 First decreases then increases

In the shown figure a particle of mass M 10 strikes the block of mass M with velocity vo and gets attached to it For what velocity vo in ms the M 10 block Bjust able to leave the ground fiyen M 100 gm K 880 N m M eeeeeee K 2M B ation

11 A 3 00 kg flowerpot is perched on a windowsill that is 8 20 m from the ground How much gravitational potential energy does the flowerpot have relative to the ground O 241 J O 201 J O 24 J O 29 4 J

a hollow cube of side a and volum V There is a small chamber of volume V 4 in the cub as shown The chamber is completely filled by m kg o water Water leaks through a hole H and spreads in the whole cube Then the work done by gravity in this process assuming that the complete water finally lies at the botton of the cube is a VIE 27 a 2 Z Hole