⚙️ 1. What is Work?
In physics, work is done when a force causes displacement in the direction of force.
📌 Formula:
Work (W) = Force (F) × Displacement (s)
👉 SI unit: Joule (J)
🔍 Conditions for Work:
Work is done only when:
- Force is applied
- Object moves (displacement occurs)
- Movement is in direction of force
❌ No work if:
- No displacement
- Force is perpendicular to motion
⚡ 2. Energy
Energy is the ability to do work.
👉 SI unit: Joule (J)
🔋 Forms of Energy:
- Mechanical energy
- Heat energy
- Light energy
- Chemical energy
- Electrical energy
- Sound energy
🚀 3. Kinetic Energy
Energy possessed by a moving object.
📌 Formula:
KE = ½ m v²
👉 Depends on:
- Mass (m)
- Speed (v)
🏔️ 4. Potential Energy
Energy stored due to position or height.
📌 Formula:
PE = m g h
👉 Depends on:
- Mass
- Height
- Gravity
🔄 5. Law of Conservation of Energy
Energy cannot be created or destroyed, only transformed from one form to another.
👉 Total energy remains constant in a closed system.
⚙️ 6. Simple Machines
A simple machine makes work easier by:
- changing direction of force
- multiplying force
- increasing speed
🔧 Types of Simple Machines:
- Lever
- Pulley
- Inclined plane
- Wheel and axle
- Wedge
- Screw
🪜 7. Mechanical Advantage
📌 Formula:
MA = Load / Effort
👉 It tells how much a machine multiplies force.
⚖️ 8. Efficiency
📌 Formula:
Efficiency = (Useful work output / Total work input) × 100
👉 No machine is 100% efficient due to friction.
🔁 9. Work-Energy Relation
- Work done = change in energy
- More work → more energy change
1. Assertion–Reason Test (20 Questions)
Instructions:
A) Both true, R explains A
B) Both true, R does not explain A
C) A true, R false
D) A false, R true
- A: Work requires displacement
R: Without displacement, work is zero
👉 A - A: Energy is conserved
R: It can neither be created nor destroyed
👉 A - A: Friction increases efficiency
R: It reduces useful output
👉 D - A: KE depends on velocity
R: KE = ½mv²
👉 A - A: Machines create energy
R: Energy is conserved
👉 D - A: Power is rate of doing work
R: P = W/t
👉 A - A: Work is scalar
R: It has magnitude only
👉 A - A: PE depends on height
R: PE = mgh
👉 A - A: Momentum is conserved
R: No external force acts
👉 A - A: Force always produces motion
R: Force can also stop motion
👉 D
2. Numericals Worksheet (10 Questions)
- F = 10N, s = 2m → Work?
👉 20 J - m = 2kg, v = 3m/s → KE?
👉 9 J - m = 5kg, h = 2m → PE? (g=10)
👉 100 J - W = 100J, t = 5s → Power?
👉 20 W - F = 15N, a = 3m/s² → mass?
👉 5 kg - m = 4kg, v = 5m/s → momentum?
👉 20 kg m/s - Load = 40N, Effort = 10N → MA?
👉 4 - Output = 80J, Input = 100J → Efficiency?
👉 80% - Force = 20N, displacement = 0 → Work?
👉 0 J - m = 3kg, v = 4m/s → KE?
👉 24 J
Fill in the Blanks (Compact Revision)
- Work = Force × ________ → displacement
- SI unit of work → Joule
- Energy is ability to do ________ → work
- KE depends on mass and ________ → velocity
- PE = m × g × ________ → height
- Force is a ________ quantity → vector
- SI unit of power → Watt
- Simple machine makes work ________ → easier
- MA = Load / ________ → effort
- Efficiency is reduced due to ________ → friction
- Energy cannot be ________ → destroyed
- Friction is a ________ force → contact
- Gravity is ________ force → non-contact
- Momentum = mass × ________ → velocity
- Work is zero if displacement is ________ → zero