Work, Energy and Power Class Notes - Yakeen Plus 2025 PDF

# YAKEEN PLUS 2025 ## Physics (ONE SHOT) - Work, energy and power - Presented by ER. MR SIR ## Topics To Be Covered 1. PhD. on Work Energy Power. ## Question 1 A block of mass M = 20 kg is dragged 5m by force F = 100N on rough horizontal surface (µ = 0.5). Match the column | Option | Force on bl...

# YAKEEN PLUS 2025 ## Physics (ONE SHOT) - Work, energy and power - Presented by ER. MR SIR ## Topics To Be Covered 1. PhD. on Work Energy Power. ## Question 1 A block of mass M = 20 kg is dragged 5m by force F = 100N on rough horizontal surface (µ = 0.5). Match the column | Option | Force on block | Work done by force on block | |---|---|---| | A | Applied(F) | Zero | | B | Normal(N) | 50 J | | C | Friction(f) | 400 J | | D | Net resultant (Fres) | -350 J | ## Question 2 A small block of mass m is kept on a rough inclined surface with inclination angle θ, fixed in an elevator. The elevator goes down with a uniform velocity v, and the block does not slide on the wedge. The work done by the force of friction on the block in time t will be | Option | Work done by the force of friction | |---|---| | A | -mgvt | | B | mgvt | | C | -mgvt sin² θ | | D | -mgvt cos² θ | ## Question 3 A man pulls a bucket full of water from h metre deep well. If the mass of rope is m and mass of bucket full of water is M, then work done by the man is | Option | Work done by the man | Explanation | |---|---|---| | A | (M/2 + m)gh | | | B | (M + m)gh/2 | | | C | (M + m/2)gh | | | D | (M + m)gh | Wext = - ΔU = 0 - (-mgh) = mgh + Mgh ## Question 4 A particle is shifted from A to B and then from B to C where A, B and C are the midpoints of the corresponding faces of a cube of side 4m. If a force F = (3î – 4ĵ + 5k) is continuously acting on the particle, then select incorrect alternative | Option | Statement| |---|---| | A | Work done from A to B is -2J | | B| Work done from B to C is -14J | | C | Work done from A to C is -16J | | D | Force F is nonconservative force | ## Question 5 Two identical balls, A and B, are released from the positions, as shown in figure. They collide elastically on the horizontal portion MN. The ratio of the heights attained by A and B after the collision will be (neglect friction) | Option | Ratio of heights attained| |---|---| | A | 1:4 | | B | 2:1 | | C | 4:13 | | D | 2:5 | ## Question 6 A block of mass 1 kg is pushed up a surface inclined to horizontal at an angle of 60° by a force of 10 N parallel to the inclined surface as shown in figure. When the block is pushed up by 10 m along inclined surface, the work done against frictional force is: [g = 10 m/s²] | Option | Work done against frictional force | |---|---| | A | 5√3 J | | B | 5 J | | C | 5 × 103 J | | D | 10 J | ## Question 7 Find work done by friction for displacement 'S'? | Option | Work done by friction | |---|---| | A | μk(mg + F sin 0). S | | B | -μk(mg + F cos 0). S | | C | μk(mg – F sin 0). S | | D | -μk(mg – F sin 0). S | ## Question 8 Match the following columns. | Option | Column I| Column II | |---|---|---| | A | Work done in pulling out a bucket from well by person and by gravitational force | Positive | | B | Work done by friction on a body sliding down an inclined plane | Negative | | C | Work done by a person in pulling a luggage on a rough surface | Positive | | D | Work done by air in bringing a vibrating pendulum to rest | Negative | ## Question 9 A particle is released from a height S. At certain height, its kinetic energy is three times its potential energy. The height and speed of the particle at that instant, respectively, are | Option | Height and speed | |---|---| | A | S / 4, √3gS /2 | | B | S / 4, √3gS / 2 | | C| S / 2, √3gS /2 | | D | S / 4, √3gS /2 | ## Question 10 In the given figure, 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 | Option | Minimum mass of A | |---|---| | A | 2M | | B | M | | C | M/2 | | D | A function of M and the force constant of the spring | ## Question 11 A ball suspended by a thread swings in a vertical plane so that its magnitude of acceleration in the extreme position and lowest position are equal. The angle (θ) of thread deflection in the extreme position will be: [27 Jan, 2024 (Shift-II)] | Option | Angle (θ) | |---|---| | A | tan-1(√2) | | B | 2tan-1(1/2) | | C | tan-1(1/2) | | D | 2tan-1(1/√5) | ## Question 12 Given below is the plot of a potential energy function U(x) for a system, in which a particle is in one dimensional motion, while a conservation force F(x) acts on it. Suppose that Emech = 8 J, the incorrect statement for this system is: [27 July, 2021 (Shift-II)] | Option | Statement| |---|---| | A | at x = x3, K. E. = 4 J. | | B | at x > x4, K. E. is constant throughout the region. | | C | at x < x₁, K. E. is smallest and the particle is moving at the slowest speed. | | D | at x = X2, K. E. is greatest and the particle is moving at the fastest speed. | ## Question 13 If a rubber ball falls from a height h and rebounds upto the height of h/2. The percentage loss of total energy of the initial system as well as velocity of ball before it strikes the ground, respectively, are: [04 April, 2024 (Shift-I)] | Option | Percentage loss of total energy and velocity | |---|---| | A | 50%, √gh/2 | | B | 50%, √gh | | C | 40%, √2gh | | D | 50%, √2gh| ## Question 14 Identify the correct statements from the following: (a) Work done by a person in lifting a bucket out of a well by means of a rope tied to the bucket is negative. (b) Work done by gravitational force in lifting a bucket out of a well by a rope tied to the bucket is negative. (c) Work done by friction on a body sliding down an inclined plane is positive. (d) Work done by an applied force on a body moving on a rough horizontal plane with uniform velocity is zero. (e) Work done by the air resistance on an oscillating pendulum is negative. Choose the correct answer from the options given below: | Option | Correct Statements | |---|---| | A | B and E only | | B | A and C only | | C | B, D and E only | | D | B and D only | ## Question 15 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:- | Option | Work done by internal forces | |---|---| | A | 1/2 (m1 + m2) u² | | B | 1/2 (m1 + m2)u² | | C | 1/2 m1u² (1 + m1/m2) | | D | 1/2 (m2 - m1)u² | ## Question 16 One of the some forces acting on a particle is conservative then :- | Option | Statement | |---|---| | A | Its work done is non zero when the particle moves exactly once around any closed path. | | B | Its work equals the change in the kinetic energy of the particle.| | C | It does not obey Newton's second law. | | D | Its work done depends on the terminal points of the motion, not on the path in between. | ## Question 17 A particle in a certain conservative force field has a potential energy given by U = 20xy/z. The force exerted on it is | Option | Force exerted | |---|---| | A | -(20y/z)î - (20x/z)ĵ + (20xy/z²)k)| | B | -(20y/z)î - (20x/z)ĵ + (20xy/z²)k | | C | -(20y/z)i - (20x/z)j - (20xy/z²)k | | D| (20y/z)î + (20x/z)ĵ - (20xy/z²)k | ## Question 18 Two blocks M₁ and M₂ having equal mass are free to move on a horizontal frictionless surface. M₂ is attached to a massless spring as shown in figure. Initially, M₂ is at rest and M₁ is moving toward M₂ with speed v and collides head-on with M2. | Option | Statement| |---|---| | A | While spring is fully compressed all the KE of M₁ is stored as PE of spring | | B | While spring is fully compressed the system momentum is not conserved, though final momentum is equal to initial momentum | | C | If spring is massless, the final state of the M₁ is state of rest | | D | If the surface on which blocks are moving has friction, then collision cannot be elastic | ## Question 19 Two inclined frictionless tracks, one gradual and the other steep meet at A from where two stones are allowed to slide down from rest, one on each track as shown in figure. Which of the following statement is correct? | Option | Statement | |---|---| | A | Both the stones reach the bottom at the same time but not with the same speed | | B | Both the stones reach the bottom with the same speed and stone I reaches the bottom earlier than stone II | | C | Both the stones reach the bottom with the same speed and stone II reaches the bottom earlier than stone I | | D | Both the stones reach the bottom at different times and with different speeds | ## Question 20 Statement-I: Friction is a non-conservative force. Statement-II: This is because work done against friction, in moving a body over a closed path, is never zero. | Option | True or False | |---|---| | | Both statements are true | ## Question 21 Statement-I: Two particles moving in the same direction do not lose all their energy in a completely inelastic collision. Statement-II: Principle of conservation of momentum holds true for all kinds of collision. | Option | True or False | |---|---| | A | Both statements are true | ## Question 22 Match the following columns. | Option | Column I| Column II | |---|---|---| | A | Erg | 1.6 x 10^-19 J | | B | Electron vole (eV) | 3.6 x 10^6 J | | C | Calorie (cal) | 10^-7 J | | D | Kilowatt hour (kWh) | 4.186 J | ## Question 23 The potential energy of a 1 kg particle free to move along the X-axis is given by U(x) = [x^4/4 - x^2/2] J. The total mechanical energy of the particle is 2 J. Then, maximum speed (in ms^-1) is | Option | Maximum speed | |---|---| | A | 3√2 | | B | √2 | | C | 1/√2 | | D | 2 | ## Question 24 Assume that in space potential energy U-depends on x-coordinate only by: U = x^3/3 - 6x^2 + 32x. A mass m can be kept on x-axis. In each position indicated in column-1, comment on the situation from column-II. | Option | Column I | Column II | |---|---|---| | | A x = 8 | P Stable equilibrium | | | B x = 2 | Q Unstable equilibrium | | | C x = 4 | R Neutral equilibrium | | | D | S Not a equilibrium | ## Question 25 Which of the following statement is correct. | Option | Statement | |---|---| | A | Kinetic energy of a system can be increased without applying external force on the system. | | B | Total work done by all the forces is equal to change in mechanical energy. | | C | Work done by static friction can't be positive. | | D | Ball projected up from a point and air resistance is not ignored then it comes at same point with more speed. | ## Question 26 Select the correct statements - (a) Potential energy is defined only for gravitational force. (b) Potential energy can be associated with frictional force. (c) Work done by spring force is equal to change in potential energy of the spring. (d) Potential energy defined as negative work done by conservative force (e) Total work done by all external force is equal to change in KE. | Option | Correct Statements | |---|---| | A | a and b | | B | a and c | | C | d, e | | D | None of these | ## Question 27 A body is moving along straight line by a machine delivering a power proportional to time: | Option | Column I | Column II | |---|---|---| | | (a) Velocity is proportional to | (i) t (time) | | | (b) Displacement is proportional to | (ii) t^2 | | | (c) Work done is proportional to | (iii) t^3 | | | | (iv) t^-1 | ## Question 28 A body of mass 2 kg begins to move under the action of a time dependent force given by F = (6ti + 6t²ĵ)N The power developed by the force at the time t is given by: | Option | Power | |---|---| | A | (6t^4 + 9t^5)W | | B | (3t^3 + 6t^5)W | | C | (9t^5 + 6t^3)W | | D | (9t^3 + 6t^5)W | ## Question 29 Block of mass M = 5 kg is kept inside a lift, which starts motion from rest in vertical upward direction with uniform acceleration (a = 4 m/sec²) | Option | Power delivered to block by force | Power (in watt) | |---|---|---| | | A By normal at 5 sec | P -500 | | | B By normal in 5 sec | Q 700 | | | C By Mg (gravity) at 5 sec | R -1000 | | | D By Mg (gravity) in 5 sec | S 1400 | ## Thank you