Is it correct to say: Assuming work is done whenever a force is applied?

If displacement is zero (holding a suitcase still) or force perpendicular to motion (coolie walking with load on head), W = 0.

Is it correct to say: Using formula PE = mgh far from Earth's surface?

PE = mgh applies only when g is nearly constant (small heights). For satellites, use PE = −GMm/r.

Is it correct to say: Confusing power and energy units?

Energy → J or kWh. Power → W or kW. 1 kWh is energy, 1 kW is power.

Is it correct to say: Taking KE as negative for a body moving backward?

KE = ½mv² is always positive because v² ≥ 0. Direction is not encoded.

Is it correct to say: Forgetting cosθ when force is at an angle?

For a pulled sledge, use W = Fs cosθ, where θ is the pulling angle.

Is it correct to say: Adding PE and KE with different reference heights?

Choose one reference level (usually ground) for all PE calculations in a problem.

Formula sheet (PDF) →

Physics · Chapter 2

Work, Energy and Power

Work, kinetic energy, potential energy, work–energy theorem, power — Maharashtra Board Class 10 Physics

8 formulas · 3 solved examples · 5 practice questions · Board weight: 4 marks · Maharashtra State Board Class 10

Not in the 2025–26 syllabus. This chapter is not part of the Maharashtra SSC (Std X) syllabus for 2025–26. It is kept here for reference.

Board Exam Tips

→Definition of 1 joule (work) and 1 watt (power) are 1-mark repeat asks.
→Derive KE = ½mv² using v² = u² + 2as — a favourite 3-mark question.
→Work–energy theorem numericals appear regularly — practise both algebraic and graphical form.
→1 kWh = 3.6×10⁶ J — commercial vs SI unit conversion is asked.
→Only the component of force along displacement does work — remember the cosθ factor.

Diagram

Force at angle θ with displacement — component F cosθ does work

Formulas(8)

Work Done by a Constant ForceBoard favourite

W = F s cos θ

Symbol	Meaning
$W$	Work done (J)
$F$	Applied force (N)
$s$	Displacement (m)
$θ$	Angle between force and displacement

Kinetic EnergyBoard favourite

K E = \frac{1}{2} m v^{2}

Gravitational Potential Energy

P E = m g h

Work–Energy TheoremBoard favourite

W_{n e t} = Δ K E = \frac{1}{2} m v^{2} - \frac{1}{2} m u^{2}

Power (Average)

P = \frac{W}{t}

Power (Instantaneous)

P = F v

Conservation of Mechanical Energy

K E + P E = constant

Commercial Unit of Energy

1 kWh = 3.6 \times 1 0^{6} J

Solved Examples

1Solved Exampleeasy3 steps

A body of mass 5 kg is lifted vertically upward through a height of 2 m. Find the work done. (g = 10 m/s²)

Force required to lift = weight of body

F = m g = 5 \times 10 = 50 N

2Solved Exampleboard4 steps

An engine pumps 100 kg of water to a height of 20 m in 10 s. Find its power. (g = 10 m/s²)

Work done against gravity

W = m g h = 100 \times 10 \times 20

3Solved ExampleHOTS4 steps

A ball of mass 0.2 kg is dropped from a height of 5 m. Find (i) PE at top, (ii) KE just before hitting ground, (iii) velocity of impact. Use g = 10 m/s². Neglect air resistance.

PE at top (reference: ground)

P E = m g h = 0.2 \times 10 \times 5 = 10 J

Traps & Common Mistakes

Common Mistakes6

1
Assuming work is done whenever a force is applied
✓If displacement is zero (holding a suitcase still) or force perpendicular to motion (coolie walking with load on head), W = 0.
2
Using formula PE = mgh far from Earth's surface
✓PE = mgh applies only when g is nearly constant (small heights). For satellites, use PE = −GMm/r.
3
Confusing power and energy units
✓Energy → J or kWh. Power → W or kW. 1 kWh is energy, 1 kW is power.
4
Taking KE as negative for a body moving backward
✓KE = ½mv² is always positive because v² ≥ 0. Direction is not encoded.
5
Forgetting cosθ when force is at an angle
✓For a pulled sledge, use W = Fs cosθ, where θ is the pulling angle.
6
Adding PE and KE with different reference heights
✓Choose one reference level (usually ground) for all PE calculations in a problem.

Practice Yourself

Practice Yourself5 questions

Q1
Calculate the KE of a car of mass 1000 kg moving with a velocity of 20 m/s.
Q2
An electric bulb of 60 W is used for 5 hours daily. Calculate the energy consumed in 30 days in kWh.
Q3
How much work is done in pushing a wall for 5 minutes if the wall does not move?
Q4
A body of mass 2 kg falls from a height of 10 m. Find its velocity just before touching the ground. (g = 10 m/s²)
Q5
Define 1 joule of work.

Notes

Work, Energy and Power — Maharashtra SSC

Maharashtra Board treats Work, Energy and Power as a compact chapter with clear formulas but tricky conceptual questions.

What counts as work?

Three conditions must hold simultaneously:

A force must act on the body.
The body must be displaced.
Force and displacement must have a component along the same line.

Positive, negative and zero work

Positive: force and displacement in the same direction (θ < 90°). Example: lifting a load.
Negative: force opposes displacement (θ > 90°). Example: friction.
Zero: perpendicular (θ = 90°) or no displacement. Example: coolie carrying weight horizontally.

Energy — many forms, one currency

Kinetic, potential, thermal, chemical, electrical, nuclear — all interconvertible. In mechanics, KE and PE dominate. In a lossless system, their sum is constant (conservation).

Power — how fast, not how much

Two engines can do the same work; the one that does it in less time is more powerful. That is why we quote engine ratings in kW or hp.

Board vs CBSE

CBSE covers this in Class 9 with similar depth. Maharashtra SSC's Class 10 treatment adds commercial unit conversion (kWh ↔ J) and slightly more numerical variety around lifts and pumps.