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- Work on an object is determined by multiplying the force applied by the distance the object moves in the direction of that force.
- The standard unit of work is the joule, where 1 joule = 1 newton * 1 meter.
- If an object does not move, the work done on it is zero.
- An object with the ability to do work is said to have energy, which is measured in the same units as work. When an object is in motion, it possesses kinetic energy, calculated as 1/2 mv2 , where m is the object's mass and v its velocity.
- Potential energy, on the other hand, arises from a change in an object's position or shape. The gravitational potential energy of an object with mass m, raised to a height h above the Earth's surface, is given by mgh.
- The law of conservation of energy states that energy can be transformed from one form to another, but it cannot be created or destroyed. The total energy remains constant before and after any transformation.
- Energy appears in various forms in nature, including kinetic energy, potential energy, thermal energy, and chemical energy. The combined total of an object's kinetic and potential energies is referred to as its mechanical energy.
- Power is defined as the rate at which work is done, and the SI unit of power is the watt, where 1 watt equals 1 joule per second (1 W = 1 J/s).
NCERT Based MCQ with Explanation:
1. Which of the following statements best defines work in scientific terms?
(a) Any activity that uses energy
(b) Moving an object using a force
(c) Force applied with displacement in the direction of force
(d) Energy exerted in any physical activity
Explanation: Work is done when a force causes displacement in the direction of the force.
2. If you push a wall and it does not move, how much work is done?
(a) Maximum work
(b) Zero
(c) Minimum work
(d) Infinite
Explanation: Work is zero if there is no displacement, regardless of the force applied.
3. The SI unit of work is:
(a) Newton
(b) Joule
(c) Watt
(d) Kilowatt
Explanation: Work is measured in joules (J), where 1 joule equals 1 newton-meter.
4. Which of the following is NOT an example of work done in scientific terms?
(a) A book lifted off the ground
(b) A car moving on a road
(c) A person pushing against a stationary wall
(d) A ball rolling down a hill
Explanation: Work requires movement in the direction of the applied force, which is absent here.
5. When the force and displacement are in opposite directions, the work done is:
(a) Zero
(b) Positive
(c) Negative
(d) Infinite
Explanation: Work is negative when the force opposes the direction of displacement.
6. A force of 10 N moves an object 5 m in the direction of the force. How much work is done?
(a) 2 J
(b) 15 J
(c) 50 J
(d) 500 J
Explanation: Work done = Force × Displacement = 10 N × 5 m = 50 J.
7. What is the work done by a force of 7 N acting over a displacement of 0 m?
(a) 7 J
(b) 0 J
(c) 14 J
(d) Cannot be determined
Explanation: Work done is zero when displacement is zero, irrespective of the force.
8. Work done by gravity on an object moving horizontally is:
(a) Positive
(b) Negative
(c) Zero
(d) Maximum
Explanation: Gravity acts vertically, so it does no work on horizontal displacement.
9. The unit of power is:
(a) Joule
(b) Watt
(c) Newton
(d) Pascal
Explanation: Power is the rate of doing work, measured in watts (W).
10. Which of the following is a correct unit conversion for power?
(a) 1 W = 1 J/s
(b) 1 W = 1 N·m
(c) 1 W = 1 J·m
(d) 1 W = 1 N/s
Explanation: Power is measured as work done per unit time, i.e., 1 watt equals 1 joule per second.
11. If an object of mass 5 kg is lifted to a height of 2 m, what is the potential energy gained? (g = 10 m/s²)
(a) 50 J
(b) 100 J
(c) 75 J
(d) 150 J
Explanation: Potential energy = mgh = 5 kg × 10 m/s² × 2 m = 100 J.
12. Which energy form is associated with motion?
(a) Potential energy
(b) Kinetic energy
(c) Chemical energy
(d) Nuclear energy
Explanation: Kinetic energy is the energy possessed by an object due to its motion.
13. An object at rest has which type of energy?
(a) Zero kinetic energy
(b) Maximum kinetic energy
(c) Infinite kinetic energy
(d) Equal potential and kinetic energy
Explanation: An object at rest has no motion, hence no kinetic energy.
14. The energy possessed by an object due to its position or configuration is known as:
(a) Kinetic energy
(b) Mechanical energy
(c) Chemical energy
(d) Potential energy
Explanation: Potential energy is stored energy based on position or state.
15. A stretched rubber band possesses:
(a) Kinetic energy
(b) Electrical energy
(c) Potential energy
(d) No energy
Explanation: Energy is stored in the stretched band due to its configuration.
16. When a force of 20 N moves an object 3 m in the direction of the force, what is the work done?
(a) 6 J
(b) 60 J
(c) 40 J
(d) 20 J
Explanation: Work = Force × Displacement = 20 N × 3 m = 60 J.
17. What happens to kinetic energy if the velocity of an object doubles?
(a) Remains the same
(b) Doubles
(c) Quadruples
(d) Triples
Explanation: Kinetic energy is proportional to the square of velocity, so doubling velocity quadruples the energy.
18. Which of the following does NOT contribute to potential energy?
(a) Height
(b) Mass
(c) Velocity
(d) Gravitational field
Explanation: Potential energy depends on height, mass, and gravity but not on velocity.
19. The energy transformation in a hydroelectric power plant is primarily:
(a) Chemical to electrical
(b) Kinetic to electrical
(c) Potential to electrical
(d) Thermal to electrical
Explanation: Water's potential energy is converted to electrical energy through turbines and generators.
20. What is the total mechanical energy of an object?
(a) Sum of kinetic and thermal energy
(b) Sum of potential and kinetic energy
(c) Sum of potential and chemical energy
(d) Only kinetic energy
Explanation: Mechanical energy combines both kinetic and potential energies.
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