Work, power & energy Questions and Answers

A body of mass m is accelerated uniformly from rest to a speed v in a time T The instantaneous power delivered to the body as a function of time is given by a O mv 2 T 7 12 2 1 mv 2 b d mv 2 T 1 mv 2 t

into the shape of an inverted U such that the horizontal part has a length 1 15 cm The bent ends of the wire are partially immersed in two pools of mercury with 2 5 cm of each end below the mercury s surface The entire structure is in a region containing a uniform 0 0065 T magnetic field directed into the page An electrical connection from the mercury pools is made through the ends of the wires The mercury pools are connected to a 1 5 V battery and a switch S When switch S is closed the wire jumps 35 cm into the air measured from its initial position Based on the facts provided answer the following questions 0 The speed A 5 2 ms C 70 cms Mercury S 15 V Mercury of the wire as it leaves the mercury is B 2 5 ms D 7 cms

A car 1000 kg is going 20 m s on a level road and slams on the brakes The skid marks are 25m long a What is the change in kinetic energy during the skid b What is the work done on the car by the road c What is the work done on the car by gravity

problem after the spring attains it s natural length Xo A m k voorr B th m 20 Maximum elongation in spring during the subsequent motion is Maximum elongation in spring during the subsequent motion is X KXO m Velocity of centre of mass of the system is Maximum speed of block A during subsequent motion be

A neutron of kinetic energy K undergoes a head on collision with a hydrogen atom at rest in ground state and is free to move k Neutron Then mark the correct option s H H atom at rest For K 20 4eV collision is perfectly elastic For K 20 4eV collision is perfectly inelastic For K 2 20 4eV collision may be elastic or it may be perfectly inelastic For K 24 18eV collision may be elastic inelastic or perfectly inelastic

Three identical discs A B and C as shown in the figure rest on a smooth horizontal plane The disc A is set in motion with velocity v after which it experiences an elastic collision simultaneously with the discs B and C The distance between the centres of the latter discs prior to the collision is 7 times greater than the diameter of each disc Find at what value of n will the disc A after the collision stops nd

Initially spring is in its natural length and blocks A B are at rest Find maximum value of constant force that can be applied on B such that block A remains at rest g 10 m s give answer in Newton k 100 N m wwwwww A 2 kg H 0 1 B 1 kg H 0 2 F

1 A truck with a mass of 40 000 kg rolls down a hill without friction from an initial height of 200 m It rolls over a 300 m long flat section with a coefficient of friction 01 and then rolls up a hill of 30 degrees with a coefficient of friction of 0 2 How far up the hill will the truck roll before coming to a stop 200 0 m P 0 0 1 300 m d 30 0 2

2 12 A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field B The work done to rotate the loop through 45 about an axis perpendicular to its plane is a zero b 3MB 2 MB c 2 d 2MB

A force F acting on an object varies with distance x as shown here The work done by the force in moving the object from x 0 to x 6 m is W J find value of 2W F N 321 2 0 3 Answer 20 08 6 x m 01 02 03 04 05 06 07 09 20 01 02 03 04 05 06 07 08 09

A 56 0 g toy car is released from rest on a frictionless track with a vertical loop of radius R The initial height of the car is h 4 a What is the speed of the car at the top of the vertical loop Use the following as necessary R and g x V b What is the magnitude of the normal force acting on the car at the top of the vertical loop N

32 A bar magnet of magnetic dipole M 51 A m is placed in region of magnetic field B 21 31 4k tesla the magnitude of torque EY les acting on magnet is C MX B 1 Zero 2 10 Nm 3 15 Nm 4 25 Nm

2 amu mass of a small atom A moves x direction from atom B which is remain stationary energy of between two particles U x 40 x at time 0 position of atom A x t 1 5 velocity of atom A v t 2 3 x direction away from B find acceleration velocity and position at t 0

A porter lifts a heavy suitcase of mass 80 kg and at the destination lowers it down by a distance of 80 cm with a constant velocity Calculate the workdone by the porter in lowering the suitcase take g 9 8 ms 2 hongo mathongo mathongo mathongo mathongo mathongo 1 62720 0 J 2 627 2 J 3 627 2 J 4 784 0 Jongo mathongo HmathongoH mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo mathongo

FL Fo 1 Fox Calculate the net work done by the force F whose variation with position has been shown as above 2 3 EIN EI Y X Xo x a hoydle 9345 8 4 All of the above Conservation of mechanical energy can be applied 5 Two identi line A 6 simultanec 50 m s F just after collision 1 20 m 3 15 m Calculate released with ano

A sphere of radius R carries charge such that its volume charge density is proportional to the square of the distance from the center What is the ratio of the magnitude of the electric field at a distance 2R from the center to the magnitude of the electric field at a distance of R 2 from the center 1 1 2 2 3 4 4 8

L A can of mass 1 kg is thrown upward which reaches a height of h 25 m from the throwing position Calculate the work done by the gravitational force as the can reaches the highest point What is the change in kinetic energy of the can What is the change in potential energy of the earth can system

5 identical balls placed on smooth horizontal surface If 1st ball moving with velocity u 2 m horizontally collide with 2nd ball and 2nd ball collide with 3rd ball and so on collisions take place If the velocity of 5th ball after collision is 1 5 Find the value of n coefficient of restitution e 1 2 u 2m sec 1 2 3 4 5

X 0374 The diagrams represent the potential energy U as a function of the inter atomic distance r Which diagram corresponds to stable molecules found in nature L 1 r 2 90 90 3 4

A mass of 18 kg moving in a straight line is brought to rest in such a way that it lose kinetic energy at uniform rate of one joule per sec If the initial kinetic energy is 900 find the distance in km travelled before coming to rest

The kinetic energy of a 2 1 kg block moving across a horizontal frictionless surface increases linearly with time according to the following eq K t 4 t How far will the object move in m between t 1 85 s and t 5 01 s

A uniform chain of mass m and length is held on a horizontal frictionless table with 1 2th of its length hanging over the edge of the table The wok done in pulling the chain up on the table is Options mgl n mgl 2n 1 2

A block of mass 2 kg is moved on a frictional horizontal plane by applying horizon of 10 N The coefficient of friction is 0 2 The kinetic energy of block after it has m distance of 10 m is Options 100 J 2 40 J B 20 J

94 In the given figure the block is moved to compress the spring by 3 2 cm from the shown natural length and released If the collision with the wall is elastic the time period of oscillation will be Here T is time period if wall would not have been there

A block of mass M is hanging from a mass less spring of spring constant k Initially the block is in equilibrium In this position length of the spring is Z Now an agent is holding a point P at a distance of from top and displaces it 3 downwards by a distance of x Find weweeeeeeee M

A particle of mass m moving with velocity v strikes elastically with a mass m at rest then the condition for maximum transfer of kinetic energy is Om m O O m m m m C

ball is placed on a smooth inclined plane of inclination 0 30 to the horizontal which is ating at frequency 0 5 Hz about a vertical axis passing through its lower end At what tance from the lower end does the ball remain at rest 1 85 m b 0 2 m c 0 42 m d 0 67 m

3 A ball of mass 10 gram and charge 107C moves from point A whose potential is 500 V to another point B whose potential is zero The velocity of the ball at the point B if its velocity at the point A is zero is 1 0 1 ms 3 10 ms G 2 0 01 ms 4 100 ms

46 In two dimensional motion instantaneous speed va is a positive constant Then which of the following is necessarily true 1 The average velocity is not zero at any time 2 Average acceleration must always vanish 3 Displacement in equal time intervals are equal 4 Equal path lengths are traversed in equal time intervals

The potential energy of a 2 kg particle free to move along the x axis is given by V x J The total mechanical energ 2 of the particle is 2 J then the maximum speed in m s is

46 A body of mass m 4 kg is acted upon by a constant 46 m 4lgt 1 force such that its position varies with time as r 1 5 The work done by the force in time interval t 1 second to t 3 second e 64 J 2 3 47 Two soap bubbles of radius 38 38 71 K T2 S bok 4 4X4 1642 1 515 and come in contact hach other Radius of curvature of the common 22100 he Si 477

A molecule of a substance has dipole mome 10 c m One mole of this substance polarised by applying a strong electric fie 10 V m If direction of electric field is sudder changed by an angle 60 then heat released the substance for the new allignment of dipoles 2 06 J 3 3 J 4 6 J

Under the action of a force F y x j an external agent takes a particle slowly along two paths as shown Path 2 is along OP and path 1 is along OAP All quantities are in SI units Then 0 Path 2 P 1 2 Path 1 The given force is non conservative Work done by along both the paths are some and the value is 2J

A particle of mass m moving in x direction with speed 2v is hit by another particle of mass 2m moving in the y direction with speed v If the collision is perfectly inelastic the percentage of the energy retained by the colliding particles after the collision is close to 1 56 3 35 2 80 4 44

A simple pendulum consists of string of length L and suspended mass m It is released from horizontal positi as shown in the figure Speed of the mass when the string becomes vertical will be m www L O 3gL O gL 2 2gL

Two blocks of masses 10 kg and 20 kg are connected by a massless spring and are placed on a smooth horizontal surface A force of 200 N is applied on 20 kg mass as shown in the diagram At the instant the acceleration of 10 kg mass is 12 ms 2 the acceleration of 20 kg mass is

A ball is dropped onto to horizontal surface from a height of 36cm After bouncing several times it comes to rest covering a total distance of 108cm measured in a vertical direction The percentage loss in kinetic energy after its first impact is 10x The value of x is

A current carrying wire has the configuration as shown in the figure Two semi infinite straight sections each tangent to the same circle are connected by a circular arc of angle along the circumference of the circle with all sections lying in the same plane What must be in radians in order for B magnetic field to be zero at the centre of the circle R

A small body a starts sliding from the height h down an inclined groove passing into a half circle of radius h 2 Assuming the friction to be negligible find the velocity of the body at the highest point of its trajectory after breaking off the groove A A 9 gh h BT 8 gh C 27 gh h 2 D 10 27 gh

For a particle constrained to move along x axis potential energy is given by U 4x 3x Then A The positions corresponding to equilibrium are x 0 and x B x C X D If the particle is released in the right neighborhood of x force after a while is ve A 8 9 corresponds to stable equilibrium corresponds to unstable equilibrium the power delivered b A

Two identical balls A and B having velocities of 0 5 m s and 0 3 m s respectively collide elastically in one dimension The velocities of B and A after the collision respectively will be NEET Phase 2 2016 1 0 5 m s and 0 3 m s 2 0 5 m s and 0 3 m s 3 0 3 m s and 0 5 m s 4 0 3 m s and 0 5 m s

A uniform chain of length L and mass M is lying on a table and 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 back on the table MgL 16 Read More MgL 32

A block of mass m at the end of a string is whirled round in a vertical circle of radius R The critical speed of the block at the top of its swing below which the string would slacken before the block reaches the top is a Rg b Rg c R g d Rg

Find the work done when a 25 kg weight is i lifted to JUE a vertical height of 2 0 m from the ground ii carried ELE TH to the same place by pushing it up an inclined plane W making an angle of 30 with the ground Take g 9 8 m s 71 2 Sjaa Ans i 490 J ii 490 J 7

Q 8 A person sitting firmly over a rotating stool has his arms folded with two identical balls stretched his arms along with balls and then the work done by him Answer A zero B Your Attempt C positive negative Correct answer Rate this

Projection of a Particle in a Potential Field Potential energy of a particle of mass m k depends on distance y from line AB according to relation U y a where k is a positive constant A particle of mass mis projected from y 3 a toward point O on line A AB Find the minimum projection speed of particle so that it will cross point O 14 Pam O E

Two men pull a rope from which a mass is hanging as shown Both apply a force of 100 N each What force should each apply to make the rope horizontal A 200 N C 600 N 230 30 B 400 N D rope cannot become horizontal

Q12 A person is carrying a box applying a force of 10N He walks horizontally across a distance of 2 m and then climbs up vertically through a distance of 5m What is the total work don him O A 0 O B 50 J O C 70 J O D 20 J

A single conservative force F x acts on 1 kg particle that moves along x axis The potential energy U x is given by U x x 2 20 Where x is in meters and U x in joules If particle has a kinetic energy of 20 J at x 5 find mechanical energy in joules at x 2m

A the figure a ball A is released from rest when the spring is at its natural unstretched length For the block B of mass M to leave contact with the ground at some stage the minimum mass of A must be mk nig F ma zelle voo A for m v 4