JEE Physics Work Energy and Power MCQs Set B

Question: A particle of mass m moving eastward with a speed v collides with another particle of the same mass moving northwards with same speed v. The two particles coalesce on collision. The new particle of mass 2m will move with velocity

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Two perfectly elastic particles A and B of equal masses travelling along the line joining them with velocity 15 m/s and 10 m/s respectively, collide. Their velocities after the elastic collision will be (in m/s), respectively

• a) 10, 15
• b) 20, 5
• c) 3, 20
• d) 0, 25

Answer: 10, 15

Question:

• a) 2 m/s
• b) 18 m/s
• c) 6 m/s
• d) 4 m/s

Answer: 2 m/s

Question: Select the false statement

• a) The momentum of a ball colliding elastically with the floor is conserved
• b) In an oblique elastic collision between two identical bodies with initially one of them at rest, final velocities are perpendicular
• c) The coefficient of restitution for a collision between two steel balls lies between zero and one
• d) In elastic collision, kinetic energy during the collision is not conserved

Answer: The momentum of a ball colliding elastically with the floor is conserved

Question: A ball of mass M moving with speed v collides perfectly inelastically with another ball of mass m at rest. The magnitude of impulse imparted to the first ball is

• a)

  

• b)

  

• c) mv
• d) Mv

Answer:

Question:

• a) + 24 J
• b) – 12 J
• c) – 6 J
• d) + 12 J

Answer:  + 24 J

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:  A chain is on a frictionless table with one fifth of its length hanging over the edge. If the chain has length L and mass M, the work required to be done to pull the hanging part back onto the table is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A bullet of mass 20 g leaves a riffle at an initial speed 100 m/s and strikes a target at the same level with speed 50 m/s. The amount of work done by the resistance of air will be

• a) 75 J
• b) 50 J
• c) 25 J
• d) 100 J

Answer: 75 J

Question:  A stone with weight w is thrown vertically upward into the air from ground level with initial speed v₀. If a constant force f due to air drag acts on the stone throughout its flight. The maximum height attained by the stone is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Figure shows the variation of a force F acting on a particle along x-axis. If the particle begins at rest at x = 0, what is the particle’s coordinate when it again has zero speed?

• a) x = 6
• b) x = 3
• c) x = 5
• d) x = 7

Answer: x = 6

Question: A spring of force constant K is first stretched by distance a from its natural length and then further by distance b. The work done in stretching the part b is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A knife of mass m is at a height x from a large wooden block. The knife is allowed to fall freely, strikes the block and comes to rest after penetrating distance y. The work done by the wooden block to stop the knife is

• a) – mg (x + y)
• b) mg (x – y)
• c) – mgy
• d) mgx

Answer: – mg (x + y)

Question: A man is running on horizontal road has half the kinetic energy of a boy of half of his mass. When man speeds up by 1 m/s, then his KE becomes equal to KE of the boy, the original speed of the man is

• a)

  

• b)

  

• c)

  

• d) 2 m/s

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A particle is moving in a circular path of radius r under the action of a force F. If at an instant velocity of particle is v, and speed of particle is increasing, then

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The kinetic energy K of a particle moving along x-axis varies with its position (x) as shown in figure

The magnitude of force acting on particle at x = 9 m is

• a) 5 N
• b) Zero
• c) 20 N
• d) 7.5 N

Answer:  5 N

Question:

• a) 5 m
• b) 2.5 m
• c) 1.25 m
• d) 1 m

Answer: 5 m

Question: If net force on a system is zero then

• a) All of these
• b) The acceleration of its a constituent particle may be non-zero
• c) Its kinetic energy may increase
• d) Its momentum is conserved

Answer: All of these

Question: Internal forces acting within a system of particles can alter

• a) The kinetic energy of the system, but not the linear momentum of the system
• b) Neither linear momentum nor kinetic energy of the system
• c) The linear momentum of the system, but not the kinetic energy of the system
• d) The linear momentum as well as the kinetic energy of the system

Answer: The kinetic energy of the system, but not the linear momentum of the system

Question: In the figure shown, a particle is released from the position A on a smooth track. When the particle reaches at B, then normal reaction on it by the track is

• a) mg
• b) 2mg
• c)

  

• d) None of this

Answer: mg

Question:  A shell at rest on a smooth horizontal surface explodes into two fragments of masses m₁ and m₂. If just after explosion m₁ move with speed u, then work done by internal forces during explosion is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A particle is moving along a vertical circle of radius R. At P, what will be the velocity of particle (assume critical condition at C)?

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:  A particle of mass m attached to the end of string of length l is released from the horizontal position. The particle rotates in a circle about O as shown. When it is vertically below O, the string makes contact with a nail N placed directly below O at a distance h and rotates around it. For the particle to swing completely around the nail in a circle,

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: If F = 2x² – 3x – 2, then select the correct statement

• a)

  

• b)

  

• c) x = 2 is the position of neutral equilibrium
• d) x = 2 is the position of stable equilibrium

Answer:

Question: When a conservative force does positive work on a body, then the

• a) Potential energy of body decreases
• b) Total mechanical energy of body decreases
• c) Total mechanical energy of body increases
• d) Potential energy of body increases

Answer: Potential energy of body decreases

Question: The variation of force F acting on a body moving along x-axis varies with its position (x) as shown in figure

The body is in stable equilibrium state at

• a) Q
• b) P
• c) R
• d) None of this

Answer:  Q

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The force required to row a boat at constant velocity is proportional to square of its speed. If a speed of v km/h requires 4 kW, how much power does a speed of 2v km/h require?

• a) 32 kW
• b) 24 kW
• c) 16 kW
• d) 8 kW

Answer:  32 kW

Question:

• a) Both
• b)

  

• c)

  

• d) None of this

Answer: Both

Question: A particle of mass m moves in a circular path of radius r, under the action of force which delivers it constant power p and increases its speed. The angular acceleration of particle at time (t) is proportional

• a)

  

• b)

  

• c) t ⁰
• d) All of these

Answer: 

Question: The rate of doing work by force acting on a particle moving along x-axis depends on position x of particle and is equal to 2x. The velocity of particle is given by expression

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Two balls of masses m each are moving at right angle to each other with velocities 6 m/s and 8 m/s respectively. If collision between them is perfectly inelastic, the velocity of combined mass is

• a) 5 m/s
• b) 2.5 m/s
• c) 10 m/s
• d) 15 m/s

Answer: 5 m/s

Question: A sphere of mass m moving with a constant velocity u hits another stationary sphere of the same mass. If e is the coefficient of restitution, then ratio of velocities of the two spheres after collision will be

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:   A neutron travelling with a velocity collides elastically, head on, with a nucleus of an atom of mass number A at rest. The fraction of total energy retained by neutron is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) 2 m/s, 2 m/s
• b) 4 m/s, 2 m/s
• c) 2 m/s, 1 m/s
• d) 4 m/s, 1 m/s

Answer: 2 m/s, 2 m/s

Question: Velocity of the ball A after collision with the ball B as shown in the figure is (Assume perfectly inelastic and headon collision)

• a)  Zero
• b)

  

• c)

  

• d)

  

Answer: Zero

Question: An object of mass M₁ moving horizontally with speed u collides elastically with another object of mass M₂ at rest. Select correct statement

• a) Momentum of M₁ is conserved in direction perpendicular to SR
• b) Momentum of M₂ will change in direction normal to CR
• c) The momentum of system is conserved only in direction PQ
• d) None of this

Answer:  Momentum of M₁ is conserved in direction perpendicular to SR

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Two bodies with kinetic energies in the ratio of 4 : 1 are moving with equal linear momentum. The ratio of their masses is

• a) 1 : 4
• b) 1 : 2
• c) 1 : 1
• d) 4 : 1

Answer: 1 : 4

Question:  A 1 kg stationary bomb is exploded in three parts having masses in ratio 1 : 1 : 3 respectively. Parts having same mass move in perpendicular direction with velocity 30 m/s, then the velocity of bigger part will be

• a)

  

• b)

  

• c)

  

• d) None of this

Answer:

Question: If kinetic energy of a body is increased by 300% then percentage change in momentum will be

• a) 100%
• b) 150%
• c) 265%
• d) 73.2%

Answer: 100%

Question:

• a)

  

• b)

  

• c)

  

• d) 1

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d) None of this

Answer:

Question: A bomb of mass 30 kg at rest explodes into two pieces of masses 18 kg and 12 kg. The velocity of 18 kg mass is 6 ms^–1. The kinetic energy of the other mass is

• a) 486 J
• b) 324 J
• c) 256 J
• d) 524 J

Answer: 486 J

Question: A ball whose kinetic energy is E is thrown at an angle of 45° with the horizontal. Its K.E. at the highest point of its flight will be

• a)

  

• b) E
• c) Zero
• d)

  

Answer:

Question: A shell of mass 200 gm is ejected from a gun of mass 4 kg by an explosion that generates 1.05 kJ of energy. The initial velocity of the shell is

• a) 100 ms^–1
• b) 120 ms^–1
• c) 80 ms^–1
• d) 40 ms^–1

Answer: 100 ms^–1

Question:  A body dropped from a height h with initial velocity zero, strikes the ground with a velocity 3 m/s. Another body of same mass is thrown from the same height h with an initial velocity of 4 m/s. Find the final velocity of second mass, with which it strikes the ground.

• a) 3 m/s
• b) 12 m/s
• c) 4 m/s
• d) 5 m/s

Answer: 3 m/s

Question:  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

• a)

  

• b) U(x) = 0
• c)

  

• d)

  

Answer:

Question: The potential energy of a system increases if work is done

• a) By the system against a conservative force
• b) Upon the system by a conservative force
• c) Upon the system by a non-conservative force
• d) By the system against a non-conservative force

Answer: By the system against a conservative force

Question: A small mass attached to a string rotates on a frictionless table top as shown. If the tension in the string is increased by pulling the string causing the radius of the circular motion to decrease by a factor of 2, the kinetic energy of the mass will

• a) Increase by a factor of 4
• b) Remain constant
• c) Decrease by a factor of 2
• d) Increase by a factor of 2

Answer: Increase by a factor of 4

Question:   The kinetic energy acquired by a mass m in travelling distance d, starting from rest, under the action of a constant force is directly proportional to

• a) m⁰
• b) m
• c)

  

• d)

  

Answer:  m⁰

Question:   A simple pendulum with a bob of mass m oscillates from A to C and back to A such that PB is H. If the  acceleration due to gravity is g, then the velocity of the bob as it passes through B is

• a)

  

• b) Zero
• c) 2gH
• d) mgH

Answer:

Question: A car moving with a speed of 40 km/h can be stopped by applying brakes after at least 2 m. If the same car is moving with a speed of 80 km/h, what is the minimum stopping distance?

• a) 8 m
• b) 2 m
• c) 6 m
• d) 4 m

Answer: 8 m

Question:  A child is sitting on a swing. Its minimum and maximum heights from the ground are 0.75 m and 2 m respectively, its maximum speed will be

• a) 5 m/s
• b) 10 m/s
• c) 8 m/s
• d) 15 m/s

Answer: 5 m/s

Question: A child is sitting on a swing. Its minimum and maximum heights from the ground are 0.75 m and 2 m respectively, its maximum speed will be

• a) 5 m/s
• b) 10 m/s
• c) 8 m/s
• d) 15 m/s

Answer: 5 m/s

Question: When a long spring is stretched by 2 cm, its potential energy is U. If the spring is stretched by 10 cm, the potential energy stored in it will

• a) 25U
• b) 10U
• c) 5U
• d)

  

Answer: 25U

Question:  A ball of mass 2 kg and another of mass 4 kg are dropped together from a 60 feet tall building. After a fall of 30 feet each towards earth, their respective kinetic energies will be in the ratio of

• a) 1 : 2
• b) 1 : 4
• c)

  

• d)

  

Answer: 1 : 2

Question: A mass of 0.5 kg moving with a speed of 1.5 m/s on a horizontal smooth surface, collides with a nearly weightless spring of force constant k = 50 N/m. The maximum compression of the spring would be

• a) 0.15 m
• b) 0.12 m
• c) 1.5 m
• d) 0.5 m

Answer: 0.15 m