Q1: A force of 50 N is applied to push a box horizontally, and it moves 4 m in the direction of the force. How much work is done? (a) 12.5 J (b) 200 J (c) 50 J (d) 46 J
Solution:
Ans: (b) Explanation: Work done equals force multiplied by displacement in the direction of force. Here, W = 50 N × 4 m = 200 J.
Q2: What is the kinetic energy of a ball of mass 0.5 kg moving with a velocity of 10 m/s? (a) 50 J (b) 5 J (c) 100 J (d) 25 J
Solution:
Ans: (d) Explanation: Kinetic energy is given by K = ½mv². Therefore, K = ½ × 0.5 × (10)² = 25 J.
Q3: A girl carries a bag horizontally over her head while walking 10 m. The upward force she applies is 30 N. How much work does she do on the bag? (a) 300 J (b) 30 J (c) 0 J (d) 3 J
Solution:
Ans: (c) Explanation: Work is zero when force acts perpendicular to displacement. Here, the upward force is perpendicular to horizontal displacement, so no work is done.
Q4: An object of mass 2 kg is lifted to a height of 5 m. What is its gravitational potential energy? (Take g = 10 m/s²) (a) 100 J (b) 10 J (c) 20 J (d) 50 J
Solution:
Ans: (a) Explanation: Gravitational potential energy is given by U = mgh. Therefore, U = 2 × 10 × 5 = 100 J.
Q5: If a machine lifts a load of 500 N using an effort of 250 N, what is its mechanical advantage? (a) 0.5 (b) 250 (c) 1 (d) 2
Solution:
Ans: (d) Explanation: Mechanical advantage is the ratio of load to effort. MA = 500 N ÷ 250 N = 2.
Fill in the Blanks
Q1: The SI unit of work and energy is the _____.
Solution:
Ans: joule
Q2: Energy possessed by an object due to its motion is called _____ energy.
Solution:
Ans: kinetic
Q3: The rate at which work is done is called _____.
Solution:
Ans: power
Q4: A _____ is a simple machine that changes the direction of force.
Solution:
Ans: fixed pulley
Q5: The sum of kinetic energy and potential energy is called _____ energy.
Solution:
Ans: mechanical
True or False
Q1: Work done is a scalar quantity and has no direction.
Solution:
Ans: True Explanation: Work is a scalar quantity. It can be positive or negative but has no specific direction associated with it.
Q2: When you push a rigid wall and it does not move, you do work on the wall in the scientific sense.
Solution:
Ans: False Explanation: No work is done on the wall because there is no displacement, even though force is applied and you feel tired.
Q3: If the velocity of an object doubles, its kinetic energy becomes four times the original.
Solution:
Ans: True Explanation: Kinetic energy is proportional to the square of velocity. If velocity doubles, kinetic energy becomes 2² = 4 times the original.
Q4: Gravitational potential energy of an object changes when it moves horizontally at the same height.
Solution:
Ans: False Explanation: Potential energy depends on height. When an object moves horizontally, height remains unchanged, so potential energy does not change.
Q5: Simple machines reduce the total amount of work required to perform a task.
Solution:
Ans: False Explanation: Simple machines do not reduce total work. They only make tasks easier by changing the magnitude or direction of applied force.
Match the Following
Column A
Column B
1. Unit of power
A. Energy due to position
2. Kinetic energy formula
B. Watt
3. Potential energy
C. Lever principle
4. Work-energy theorem
D. ½mv²
5. F₁ × d₁ = F₂ × d₂
E. W = ΔE
Solution:
Ans:
1 - B: The SI unit of power is watt, named after James Watt who invented an efficient steam engine.
2 - D: Kinetic energy is given by the formula K = ½mv², where m is mass and v is velocity.
3 - A: Potential energy is the energy stored in an object or system due to its position or deformation.
4 - E: The work-energy theorem states that work done on an object equals the change in its energy.
5 - C: The principle of lever states that effort multiplied by effort arm equals load multiplied by load arm.
Short Answer Questions
Q1: Explain what is meant by work in the scientific sense and state its SI unit.
Solution:
Ans: In science, work has a precise meaning. Work done on an object equals the force applied multiplied by displacement in the direction of force. It is expressed as W = F × s. The SI unit of work is the joule (J), where 1 joule equals 1 newton-metre, or 1 J = 1 kg m² s⁻².
Q2: Under what three conditions is the work done on an object equal to zero?
Solution:
Ans: Work done is zero when: (1) The force acting on the object is zero. (2) There is no displacement, even if force is applied, such as pushing a rigid wall. (3) The force acts perpendicular to displacement, like carrying a box horizontally while applying upward force.
Q3: State the law of conservation of mechanical energy and give an example.
Solution:
Ans: The law states that the mechanical energy of an object is conserved if no external forces like friction or air resistance act on it. For example, in a freely falling object, potential energy decreases while kinetic energy increases, but total mechanical energy remains constant throughout the fall.
Q4: What is a simple machine? How does it help us perform tasks more easily?
Solution:
Ans: A simple machine is a device that helps perform work against gravity or other forces more easily. It does not reduce total work done but changes the magnitude or direction of applied force. Examples include pulleys, levers, and inclined planes, which reduce effort needed or change force direction.
Q5: Distinguish between positive work and negative work with one example each.
Solution:
Ans: Positive work occurs when displacement is in the same direction as force, such as pushing a wheelchair forward. Negative work occurs when displacement is opposite to force direction, such as a goalkeeper stopping a ball where applied force opposes the ball's motion. Work can be calculated accordingly.
Long Answer Questions
Q1: Derive the expression for kinetic energy of an object and explain how it changes with velocity.
Solution:
Ans: Consider an object of mass m starting from rest (u = 0) acquiring velocity v under constant force F over displacement s. From kinematics, v² = 2as, so s = v²/(2a). Work done is W = F × s = ma × v²/(2a) = ½mv². By work-energy theorem, this appears as kinetic energy. Thus K = ½mv². Kinetic energy is proportional to the square of velocity, so doubling velocity increases kinetic energy four times.
Q2: Explain the energy transformations that occur in a simple pendulum and why it eventually stops swinging.
Solution:
Ans:
At extreme positions, the pendulum bob is at rest with maximum potential energy and zero kinetic energy.
As it moves toward the centre, potential energy converts into kinetic energy.
At the lowest point, kinetic energy is maximum and potential energy is minimum.
Energy converts back to potential as it rises again, maintaining total mechanical energy constant.
In reality, it stops due to energy loss from air resistance and friction.
Q3: Analyse how an inclined plane provides mechanical advantage and derive its expression.
Solution:
Ans: An inclined plane helps move heavy loads to higher levels using smaller force over larger distance. Let mass be m, incline length L, height h, and effort F'. Work done by effort is F' × L, and potential energy gained is mgh. By work-energy theorem, F' × L = mgh. Therefore, mechanical advantage MA = mg/F' = L/h. Since L is greater than h, MA is greater than 1, meaning effort required is reduced proportionally.
Energy, and Simple Machines, Viva Questions, Important questions, shortcuts and tricks, and Simple Machines, video lectures, Free, pdf , Sample Paper, Energy, past year papers, and Simple Machines, Objective type Questions, Summary, study material, Exam, MCQs, Previous Year Questions with Solutions, Extra Questions, Worksheet with Solutions: Work, ppt, practice quizzes, Energy, Worksheet with Solutions: Work, Worksheet with Solutions: Work, Semester Notes, mock tests for examination;
