Work, power & energy Questions and Answers

has significant 5 If a amplitude upto a factor of 1 e of original only in the period betweent 0 stot ts then t may be called the average life of the pendulum When the spherical bob of the pendulum suffers a retardation due to viscous drag proportional to its velocity with b as the constant of proportionality the average life time of the pendulum is assuming damping is small in seconds a 0 693 b 2 c 1 1 0 b b d b 6 Hydrogen atom is excited from ground state to another state with principal quantum number equal to 4 Then the number of spectral lines in the emission spectra will be a 2 b 3 c 5 d 6

One mole of a monoatomic gas is carried along process ABCDEA as shown in the diagram Find the net work done by gas p Nm f sothia PB TA 07 0 2 1 1 3 1 160 0 1 T B A Di 1 2 E 3 4 V m dol

On a horizontal surface a 300 gram object glides 80 cm If the coefficient of kinetic friction is 0 20 how much work is required to overcome friction between the object and the table

A particle moves under the influence of the force F yi zj xk N along the edges of a unit cube edge length 1m on the path OA AB BC CD DE EO Then the A Total work done is zero Z E A D B B Total work done is 1 joule D Faroo E is conservative

Two springs of spring constants k and k are connected in series such that one end is fixed and the other is connected to a block of mass M as shown in figure The block is pulled to right from its equilibrium position by a distance xo and released select the correct alternative s F Audic k au k f nt ch suf 33 a A at Mt s fa i zef guz M Gwala gch u a fhu q 1 gch c 34 44 FA Geff 32 A ach Ga Ga am Xo Ga ad faccu facru chi aua MR A B A C A D k 00000 K ooooo M Displacement of A is xo Displacement of A is k1x0 k k2 Displacement of A is k x0 k k2 Correct Answer xo 2 k xo k k2 k2x0 k k2 Time period of resulting oscillatory M k1 k kjk motion of the block is 2TV zh Hukum a d hid

The force acting on a particle constraint to move along y axis varies as shown below F 7 Consider the following statements a Point E is of stable equilibrium b Point A is of unstable equilibrium Choose the correct statement 1 Only a 3 Both a and b 2 Only b 4 Neither a nor b

The gravitational potential difference between the surface of a planet and 10 m above is 5 J kg If the gravitational field is supposed to be uniform the work done in moving a 2 kg mass from the surface of the planet to a height of 8 m is 1 2 J 2 4J 3 6 J 4 8 J

of distance is given as U x 6x 2x The conservative force acting on body x 1 m will be NCERT Pg 1 1 6 N 3 10 N 2 8 N 4 12 N

Due to a push the collar of mass mis sliding down at a speed vo on the fixed circular ring when it passes through the point A The ring is frictionless A spring of spring constant k and relaxed length Ris also pulling the collar Yachi 27 92 m GwHI A hidz Gid qau adu V ute Mudd gy far A guza 1 aau adusa 1 M Audich faxia Rad yg ca 1 g mmmmmmmmmmmm A Collar chick AR RUT 0 The acceleration of the collar at A is R 3 4 R B The force on the collar by the ring when mv kR R it passes point A is kR mv kR R D A gurd aa dau HA SA uz da Correct Answer 2 C lowest point is 2gR 2 1 V m j c mz Aha fa g uz u adi ad su un v 2gR 2 1 The speed of collar when it reaches the 2kR 2kR m Correct Answer The acceleration of collar when it reaches the lowest point is zero

Question 1 1 point A 2500 kg truck travelling at 72 km h slams on the brakes and skids to a stop The frictional force from the road is 7900 N Use the relationship between kinetic energy and mechanical work to determine the distance it takes for the truck to stop Each question answered is worth K 4 T 6 C 8 A6

Work done to carry bob upto angle 60 with the vertical vary slowly from initial vertical position is Given g 10 ms 2 1 5 3 J 1 m 60 1 kg 2 10 J 5 4 J

250 gram falls from a tree through a vertical distance of 6 m and reaches the ground with a velocity 8 m s If it experiences a constant air resistance during its fall then the magnitude of work done by the air resistance on it is g 10 m s A 8 J B 7 J C 23 J D 15 J

Loss of energy between C and D A 2 25 kg block is placed at position A on the 4 10 m track path CD of the track are frictionless while path A and path BC are rough with a coefficient of friction of 0 280 The length of BC is 1 20 m The block starts from rest at A and stops at D 1 20m D

A position dependent force F acting on a particle and its force position curve is shown in the figure Work do on the particle when its displacement 0 to 5 m is F N 10 1 35 J 3 15 J 10 2 4 25 J 5 J x m

4 May 175 A small ball is given a velocity 2g smooth horizontal floor which leads to a smooth vertical circular path The ball will Q P A 71 2 Jzgl Smooth Jyl 1 Complete the loop 2 Reach only upto point P 3 Reach to point Q 4 Leave the contact somewhere between P and Q

267 Work done by the external agent in increasing the length of spring from natural length 10 cm to 10 1 cm is 20 J Work done by the agent in increasing the length from 10 1 cm to 10 2 cm is 1 20 J 2 40 J 24x2 3 60 J 4 100 J 4 A

N acts on a elocity of the power of the 1 1 0 vertical circle netic energy 90 A particle suspended by a light inextensible thread of length is projected horizontally from its lowest position with velocity 4g The particle will leave the circular path at a height from its lowest position 1 3 12 2 3 41 3 2 51 3 4 21

A particle of mass 5 kg moving in the X Y plane has its potential energy given by U 7x 24y Joule The particle is initially at origin and has velocity u 14 4t 4 2 m s D the particle has speed 25 m s at t 4sec the particle has an acceleration 5 m s the acceleration of particle is normal to its initial velocity none of these

A bob is suspended from a peg on a wall by a massless string of length L If it is given a velocity 2gL at the lowest point then angular amplitude with which body will oscillate is 1 60 2 90 3 75 4 30

M with a constant downward acceleration of Then power delivered by the rope at any time t Mg t Mg 9 9 4 2 Mg t 57 A rope is used to 1 3 2 Mg t 2 t

3 30 J 131 A body of mass 5 kg at rest is dropped from the top of a 20 m tower If the body reaches the ground at 10 m s then work done by air resistance is 1 750 J 3 750 J 2 250 J 4 250 J

c kinetic energy decreases Q 33 Dimension of k m is here k is force constant a c T T d b d kinetic energy increas T 2 T 1

Case 1 Read the case study given below and answer the following questions from 31 to 35 Potential energy is the energy stored within an object due to the object s position arrangement or state Potential energy is one of the two main forms of energy along with kinetic energy Potential energy depends on the force acting on the two objects Q 31 A body is falling freely under the action of gravity alone in vaccum Which of the following quantities remain constant during the fall Kinetic energy a c mechanical energy b d Potential energy none of these

v u at is applicable when an acceleration a is uniform Reason Q 26 No work is done when a the displacement is zero c the force and displacement are mutually perpendicular b d the force is zero all of the above

mechanical energy Q 32 Work done by a conservative force is positive if a potential energy decreases c kinetic energy decreases c d b d none of these potential energy increases kinetic energy increases

A constant 113 N force acts on a 3 92 kg box The box initially is moving at 10 8 m s in the direction of the force and 4 73 s later the box is moving at 88 5 m s Determine the work in J done by this force You may assume that the box experiences constant acceleration but do not assume that only one force acts on the box

134 A ball of mass 1 kg is thrown horizontally from the top of a tall tower with velocity v 81 m s The change in gravitational potential energy of the ball earth system in 4 s will be 1 800 J 3 160 J As 2 320 J ation nel 4 200 J

62 Which of the following pair s binding energy 1 Two point masses each of mass m at distance d Nd 2 Two solid spheres each of mass m with their centres at distance d 3 A point mass and a solid sphere each of mass m at distance d 4 All above pairs have same potential energy

A block of mass 1 0 kg moving on a horizontal surface with speed 2 m s enters a rough surface The retarding force F on the block is given by k F 10m x 100 m F 0 x 10 m and x 100 X m where k 0 5 J The kinetic energy of the block at x 100 m is 1 4 5 J 3 0 85 J 2 2 5 J 4 1 5 J

A 20 kg block attached to a spring of spring constant 5 N m is released from rest at A The spring at this instant is having an elongation of 1 m The block is allowed move in smooth horizontal slot with the help of a constant force of 50 N in the rope as shown The velocity of the block as it reaches B is assume the rope to be light 50N 4 m s 2 m s O 1 m s 3 m r ooooo 4m4 B 3m

A ball of mass M is released from angle 0 as shown and meets a peg P that is fixed on the wall as shown and moves in a ci thereafter What is the maximum value of cose for it to complete the circle if the dimensions of the peg are negligible O 0 07 O 0 06 O 0 05 0 04 M P Save

A particle with total energy E is moving in a potential energy region U x Motion of the particle is restricted to the region when KN NEET 2013 examsnet com O U X OU x 0 OU x E Q x E

An automobile of mass m starts moving along a straight track at time t 0 under a constant power P choose correct option s Velocity of automobile after timetis IN ATX Net force on automobile after time t is 2Pt m mp N2t Displacement of automobile after time tis 8Pt3 9m Kinetic energy of automobile after time this Pt

21 A body of mass M just starts sliding down on the inclined plane when the angle ZACB 30 as shown in figure The coefficient of kinetic friction is 1 17 1 2 3 AZ M 309 C B 2 2

A rod of length 2m is maintained to rotate with a constant angular velocity 1 rad s about a vertical axis passing through one end fig There is a spring of spring constant k 1 N m which just encloses rod inside it in natural length One end of the spring is attached to axis of rotation S is a sleeve of mass m 0 4kg which can just fit on the rod All surfaces are smooth With what minimum kinetic energy in J sleeve should be projected so that it enters on the rod without impulse and completely compresses the spring

1 A spring has force F kx where k is the spring constant and x is the displacement from its unstretched position For the sys shown a mass m connected to an unstretched spring initially at rest how far does the spring extend before the system moment comes to rest Assume that all surfaces are frictionless and that the pulley is frictionless as well O O O 3mg 2k mg k 2mg k mmmmmm 30 X

A galvanometer of resistance 50 2 is connected to a battery of 3 V along with a resistance of 2950 S in series A full scale deflection of 30 divisions is obtained in the galvanometer In order to reduce this deflection to 20 divisions the resistance in series should be AIPMT Prelims 2008 1 4450 S 2 5050 S 3 5550

Question No 10 A system consists of two identical slabs each of mass m linked by compressed weightless spring of stiffness K as shown in figure The slabs are also connected by a thread which is burnt at a certain moment Find at what minimum value of the initial compression x o spring the lower slab will bounce up after the thread is burned through m mg 2K O mg lllllll m K

A block whose mass is 500 g is fastened to a spring The spring has spring constant of 100 N m The block is pulled to a distance of x 10 cm from its equilibrium position state of x 0 from rest at t 0 What is kinetic energy of block at x 5 cm NCERT Pg 347 1 0 375 J 056 2 0 19 J IA

Pls explain why we need to substract 280 60 kg as give in ncert il 1 1 8 10 N Example 9 3 In a human pyramid in a group is supported by the legs of a circus the entire weight of the balanced performer who is lying on his back as shown in Fig 9 5 The combined mass of all the persons performing the act and the tables plaques etc involved is 280 kg The mass of the performer lying on his back at the bottom of the pyramid is 60 kg Each thighbone femur of this performer has a length of 50 cm and an effective radius of 2 0 cm Determine the amount by which each thighbone gets compressed under the 1 A Us thi d O 9

A 30 metre deep well is having water up to depth of 15 m An engine evacuates it in one hour The average power of the engine if the diameter of well is 4 m will be 10 kW P 9 5 kW 11 55 kW 12 6 kW Solution Answer 3 Mass of water V p h x p x 2 x 15 x 1000 30 15 h 2 W mgh 22 5 m 4x15x1000 9 8 22 5

A weightless piston divides a thermally insulated cylinder into two parts of volumes V and 3V 2 moles of an ideal gas at pressure P 2 atmosphere are confined to the part with volume V 1 litre The remainder of the cylinder is evacuated Initially the gas is at room temperature The piston is now released and the gas expands to fill the entire space of the cylinder The piston is then pressed back to the initial position the increase of internal energy in the process is given by n 100 then n The ratio of the specific heat of the gas y 1 5

A machine gun fires bullets of 50 gm at the speed of 1000 m sec If an average force of 200 N is exerted on the gunner the maximum number of bullets fired per minute is 1 240 2 120 4 30 3 60 The Newton s laws of motion are valid in

A man weighing 60 kg climbs up a stair case carrying a 20 kg load on his head The stair case has 20 steps and each step has a height of 20 cm If he takes 10 sec to climb calculate the power in watt take g 10 m s

8 A particle is acted upon by constant forces F 21 35 4k and F 2j 3k is displaced from the point A 2 1 0 to the point B 3 4 2 Find the total work done by these forces Ans 2 units

A particle is acted upon by a force F which 37 varies with position x as shown in figure If the particle at x 0 has kinetic energy of 25 J then the kinetic energy of the particle at x 16 m is 110 F N 5 0 5 10 1 45 J 24 168 2 30 J 10 12 14 16 xim 3 70J 4 20 J za at fax fa sigur feffafda start af x 25 J x 16 m 110 F N 5 0 10 1 45 J 2 30 J 10 14 16 x m 3 70J 4 20 J

5 A small solid sphere A rolls without slipping inside a large fixed hemispherical bowl of radius R as shown in figure If the sphere starts from rest at the top point of the hemisphere find the normal force exerted by the small sphere on the hemisphere when it is at the bottom B of the hemisphere 17 A 7 m B mg R B c m B mg

A bomb of mass 6 kg initially at rest explodes in to three identical fragments One of the fragments moves with a velocity of 10 31 m s another fragment moves with a velocity of 10 m s then the third fragment moves with a velocity of magnitude A 30 m s B 20 m s C 15 m s D 5 m s

A vertical force Does not work on a horizon tally displaced object this is because the dis placement of the object in the the direction of the force is zero Why is it zero and why does the force not w ork

Physics Question No 29 Two blocks A and B of equal mass m 1 0 kg are lying on a smooth horizontal surface as shown in figure A spring of force constant k 200 N m is fixed at one end of block A Block B collides with block A with velocity 2 0 m s The maximum compression of the spring will be 2 0 m s B oooooo A Question Palette www