Work, power & energy Questions and Answers

The figure shows two equal positive charges each of magnitude 50 C fixed at points 3 0 m and 3 0 m respectively A charge 50 C moving along negative y axis has a kinetic energy of 4J at the instant it crosses point 0 4 m If the y co ordinate of this charge where direction of its motion reverses for the first time after crossing this point is x 2 m then x is neglect gravity 0 4 50 C 3 0 50 C 0 3 0 50 C X

A body of mass 2kg is moving with velocity 10m s towards east Another body of same mass and same velocity moving towards north collides with former and coalsces and moves towards north east Its velocity is

Q16 A body of mass 5kg is suspended by a spring balance on an inclined plane as shown in figure The spring balance measure 125 a 50 N b 25 N c 500 N d 10 N

Work in Charge Transportation A point charge q is isolated at the centre O of a hollow metal shell of inside radius a and outside radius b The shell is uncharged and provided with a small orifice Find the amount of work required to be done in transporting the charge from centre O to infinity through the orifice shown in figure Wext Uf Ui n 1 of 9

The string of pendulum of length is displaced through 90 from the vertical and released Then the minimum strength of the string in order to withstand the tension as the pendulum passes through the mean position is Question Type Single Correct Type 1 mg 2 3 mg 3 5 mg 4 6 mg

A deliveryman moves 10 cartons from the sidewalk along a 10 meter ramp to a loading dock which is 1 5 meters above the sidewalk If each carton has a mass of 25 kg what is the total work done by the deliveryman on the cartons to move them to the loading dock Question Type Single Correct Type 1 2500 J 2 3750 J 3 10000 J

Three vessels A B and C of different shapes contain water upto the same height as shown in the figure P P and Pc be the pressures exerted by the water at the bottom of the vessels A B and C respectively Then A B Question Type Single Correct Type 1 PA PB Pc C 2 PB PC PA

A solid cylinde inextensible light string and is placed on a rough inclined plane as shown in the figure The frictional force acting between the cylinder and the inclined plane is 60 The coefficient of static friction is 0 4 7 1 mg 2 2 5 mg

A projectile is fired from the surface of the earth of radius R with a velocity KVe where Ve is the escape velocity from the surface of the earth and K 1 The maximum height of rise from the centre of earth is Question Type Single Correct Type 1 R K 1 2 K R 3 R 1 K

A body of mass 1 kg begins to move under the action of a time dependent force F 2ti 3t j N where and are unit vectors along x and y axis What power will be developed by the force at the time t NEET 2016 1 2 3t5 W 3 21 2 444 W 2 2 2 3f 2 W 4 213 34 W

A uniform rope has mass m and length 1 It is held on a frictionless table with one sixth of its length o hanging over the edge The work done in jus pulling the hanging part back on the table is 1 3 mgl 72 mgl 12 x 4 mgl 36 mgl woold 6

5 M M A body is displaced from 0m 0m to 1m 1m along the path x y by a force F x yi N The work done by this force will be 2 J Two charged capacitors have their outer plates fixed and inner plates connected by a spring of force constant k the magnitude of charge on cach capacitor is q and sign of charge is shown in figure Find

A bullet of mass 10 g moving horizontally with a velocity of 400 ms 1 strikes a wood block of mass 2 kg which is suspended by light inextensible string of length 5 m As a result the centre of gravity of the block found to rise a vertical distance of 10 cm The speed of the bullet after it emerges out horizontally from the block will be 1 100 ms 1 3 120 ms 1 NEET Phase 2 2016 2 80 ms 1 4 160 ms 1

61 A Work and energy have the same units in any given system of measurement B Work and power have the same ratio of S unit to CG S unit 1 Statement A is true and B is false 2 Statement A is false and B is true 3 Both A and B are true 4 Both A and B are false

D A truck moving on horizontal road with contant acceleration of 2m s2 A block of mass 2 kg kept inside truck An observer also stands at rest in the truck then work done by pseudo force on block in 5 sec will be There is no relative motion between truck and block 1 50J 2Kg 2 50J a 4

5 Two particles of equal mass m are connected by a spring of spring constant K kept on a smooth floor Each of the bodies are given equal speed v in the opposite direction Calculate the maximum compression of the spring 1 V 2m k m

2 2 A block m 0 5 kg slides down a frictionless inclined plane 2 m long as shown in figure 2 196 It then slides on a rough horizontal table surface of 0 3 for 0 5 m It then leaves the top of the table which is 1 0 m high How far from the base of the table does the block land m 30 A Figure 2 196

7 A body of mass m is tied to a string to top of a trolley moving with an acceleration a Calculate the maximum angle the string will make with the vertical Tsino m 1 tan an a 2 2tan 3 a 0 g 1 tan 2 a g TanT m Ts a

If a small sphere of mass m and charge q is hung from a silk thread at an angle with the surface of a vertical charged conducting plate then for equilibrium of sphere the surface charge density of the plate is A mg 9 tan 0 C mgq tan 0 B D 2mg 9 mg 3q tan 0 tan 0

Power of a Force Pulling a Rope Figure shows a rope resting on rough ground One end A of rope is pulled by an external force such that it moves at a uniform speed v If mass per unit length of rope is kg m find the power associated with the external force pulling the rope Assume there is no slipping of rope on ground v

A drop of water of mass m 0 4 g is placed between two clean glass plates the distance between which is 0 01 cm If the force needed to hold one of the plates is 3 2x N find x Surface tension of water 0 08 N m

A drum of radius R and mass M rolls down without slipping along an inclined plane of angle e The frictional force 1 Dissipates energy as heat 2 Decreases the rotational motion 3 Decreases the rotational and translational motion 4 Converts translational energy to rotational energy

Question37 For the given diagram mark the correct option s Given that Neglect any Friction B 0000 4 subsequent motion is 9 mA mB mv Options a for e 1 for collision between blocks A B maximum Kinetic Energy for block C in 2 2m 3k Vo m b for e 1 for collision between block A B maximum compression in spring c If A sticks with B after collision then maximum Kinetic energy for block C in subsequent mv

The spring has a length of 1 5 m and the 10 kg block is at rest on the incline when a force of F 100 N is applied to the block parallel to the plane Determine the velocity of the block after it moves 1 m down the plane The unstretched length of the spring is 1 0 m The coefficient of friction between the plane and the block is x 0 20 and the spring has a stiffness k 80 N m F 100 N 30

A boy is holding one end of an inextensible cord supporting a block of mass m at its lower end From this block another block of mass Mis suspended with the help of a light spring of stiffness k The boy brings the assembly over a table and lowers it until the lower block touches the tabletop and then releases the cord How far will the upper block move before coming to an instantaneous rest first time

One end of a light spring of force constant k is fixed to the ceiling The other end is fixed to a block of mass m Initially the spring is relaxed The work done by an external agent to lower the hanging body of mass m slowly till it comes to equilibrium is B 3 m g 2 k m g 2 k m 0 3 Correct Answer

A ball is projected with initial velocity 40 2 m s at an angle of 60 with horizontal as shown in figure When its velocity is making an angle of 45 with downward vertical it collides a vertically hanging ball of same mass and sticks to it as shown in figure Find the maximum value of length in m of the string so that the combined mass completes the vertical circle in subsequent motion 40 2m s 60

4 In a common emitter CE amplifier having a voltage gain G the transistor used has transconductance 0 03 mho and current gain 25 If the above transistor is replaced with another one with transconductance 0 02 mho and current gain 20 the voltage gain will be NEET 2013 1 1 5 G 1 2 G 3

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

An asteroid is moving along a straight line A force acts along the displacement of the asteroid and slows it down The asteroid has a mass of 4 7x 10 kg and the force causes its speed to change from 6500 to 4700m s a What is the work done by the force b If the asteroid slows down over a distance of 1 2x 10 m determine the magnitude of the force a Work b F

A body of mass 2 kg is moving along y axis with velocity 10 m s Impulsive force shown in the figures acts on it along x axis Work done by this impulsive force is F KN 50 251 ms Correct Answer

A DC motor operates with 220V mains Initially it draws a current of 20A The resistance of starter is 60 When the motor runs at its full speed it consumes 500 W power Find the current drawn by it 1 5A 3 15A 4 20A 2 10A

A 1 80 kg block slides on a rough horizontal surface The block hits a spring with a speed of 2 00 m s and compresses it 11 0 cm before coming to rest If the coefficient of kinetic friction between the block and the surface is 0 560 what is the force constant of the spring in N m 215 425 415 225

Mass input Energy input Energy Output Mass Output Open System The open given in the schematic diagram below mass energy entropy and exergy balance of the system Write down the equations mass heat and energy transfer with work

n elastic ball are placed at rest on a smooth horizontal plane which is circular at the end with radius R m m 2 2 as shown in the figure The masses of the ball are m minimum velocity which should be imparted to the first ball m such that the nth ball will complete the vertical circle 1st nth m 2n 1 respectively Find the RA

A 2 kg object is released from rest from a height of 3 m above Earth s surface How much kinetic energy does the object have when it reaches a height of 1 m A 2 5 J B 10 J C 20 J D 30 J E 40 J

Electrons with energies of 1 0 eV and 2 0 eV are incident on a barrier 10 0 eV high and 0 50 wide a Find their respective transmission probabilities b How are these affected if the bas is doubled in width

A force of 40 N is applied on a body of mass 4 kg resting on horizontal plane The body gain a kinetic energy 20 J after it move distance 2 m The frictional force is 20 N 30 N 25 N 10 N

The work done in moving a particle from point 2 2 to 4 5 in X Y plane and in a force field with potential energy U k y is 3k 2k 5k k

A 100 g ball moving to the right at 4 0 m s collides head on with a 200 g ball that is moving to the left at 3 0 m s If the collision is perfectly inelastic what is the speed of the combined balls after the collision What is the direction of the combined balls after the collision

A bob of mass m suspended by a string of length is given a minimum velocity required to complete a full circle in the vertical plane At the highest point it collides elastically with another bob of mass m suspended by a string of length 12 which is initially at rest Both the strings are mass less and inextensible If the second bob after collision acquires the minimum speed required to complete a full circle in the vertical plane the ratio 1 12 is

A uniform metal rod is suspended from one end Wher it is displaced through 60 from downward vertical the change in potential energy is U The further change in potential energy when it is displaced further 30 is U 2U 4U 3U 2

A particle is acted upon by a constant power Then which of the following physical quantity remains constant Speed Rate of change of acceleration Rate of change of kinetic energy Kinetic energy

A person of mass 50 kg standing on a smooth horizontal plane of ice throws a body of mass 5 kg with velocity 10 m s Then the total kinetic energy of person and body is 275 J 150 J 300 J 375 J

6 A block of mass 2 0 kg kept at rest on an inclined plane of inclination 37 is pulled up the plane by applying a constant force of 20 N parallel to the incline The force acts for one second a Show that the work done by the applied force does not exceed 40 J b Find the work done by the force of gravity in that one second if the work done by the applied force is 40 J c Find the kinetic energy of the block at the instant the force ceases 2 1 10 m s

6 In Fig B the pin P sliding without friction in the slotted bar OA moves with constant velocity vo along the horizontal x axis causing the bar OA to rotate in the vertical plane about the fixed axis through O For the particular instant when 0 30 find the force F that the pin exerts on the bar The following numerical data are given W 5 lb 1 20 in vo 30 ips Ans F 1 29 lb 9 A right circular drum of radius r and weight W rotating at 600 rpm is braked by the device shown in Fig C Develop a formula for the time t required to bring the drum to rest if the coefficient of friction between the drum and breaking bar is u The following data are given 4 ft a 2 5 ft r 15 in 0 25 W 400 lb and P 100 lb Ans t 12 2 sec WALL 12 10 A solid right circular drum of radius r 1 ft and weight W 32 2 lb is free to rotate about its geometric axis as shown in Fig D Wound around the circumference of the drum is a flexible cord carrying at its free end a weight Q 10 lb If the weight Q is released from rest a find the time t required for it to fall through the height h 10 ft b With what velocity v will it strike the floor Ans a t 1 275 sec b v 15 7 fps B 2 FIG B 7 A shaft of radius r rotates with constant angular speed in bearings for which the coefficient of friction is u Through what angle will it rotate after the driving torque is removed Ans 0 ro 4 g A 8 The wheel of a small gyroscope is set spinning by pulling on a string wound around the shaft Its moment of inertia is I 0 05 lb sec in and the diameter of the shaft on which the string is wound is 1 2 in If 30 in of string is pulled off with a constant force of 12 lb what angular velocity will be imparted to the wheel Ans 120 rad sec Q FIG C FLERES h

A uniform chain of length I and mass m is placed on a smooth table with one fourth of its length hanging over the edge The work that has to be done to pull the whole chain back onto the table is A B 1 H 0 mgl mgl Correct Answer Your Answer

76 A massless spring k 800 N m attached with a mass 500 g is completely immersed in 1kg of water The spring is stretched by 2cm and released so that it starts vibrating What would be the order of magnitude of the change in the temperature of water when the vibrations stop completely Assume that the water container and spring receive negligible heat and specific heat of mass 400 J kg K specific heat of water 4184 J kg K 9 April 2019 Evening A 10 K B 104K C 10 K D 10 5K

A 10 kg block is gently put on a moving plank with velocity 1 m s on a frictionless horizontal ground surface And in due time the block starts with the plank at 1 m s The work done by the external force which maintains the constant speed of Planck The coefficient of friction between plank and the block is 0 4 take g 10 m s A 100 J C 10 J B 50 J D 5 J

A body of mass 1 0 kg initially at rest is moved by a horizontal force of 0 5 N on a smooth frictionless table Calculate the work done by the force in 10 s B C D 12 5 J 10 3 J 14 3 J 11 3 J 4 Your Answer