Question

Work and energy

Notes and Important notes
Class 9
Science​ .

Answer 1

Work

Definition : Work is said to be done when a force applied to an object moves that object.

Formula : We can calculate work by multiplying the force by the movement of the object.

W = F × d

Unit: The SI unit of work is the joule (J)

Energy

Definition: In physics, we can define energy as the capacity to do work.

Formula: For the potential energy the formula is

P.E. = mgh

Unit: The SI unit of energy is joules (J), which is named in honour of James Prescott Joule.

Answer 2

Answer :

$\boxed{Work\;and\;Energy}$

Work :-

• Work is said to be done only when the force applied on a body makes the body move, i.e., if there is a displacement of the body.
• The amount of work of a body depends on two factors, i) the magnitude of force applied, ii) the displacement produced by the force.
• Work = Force × displacement of the point of application of force in the direction of force
• W = F × S (mgh)
• S.I. unit of work is joule (J).
• 1 joule = 1 newton × 1 metre.
• Work is a scalar quantity, no direction but has magnitude.

Energy :-

• The energy of a body is the capacity to do work.
• Energy spent does not depend on time.
• There is not transfer of energy is a body is acted upon by a force normal to the direction of its displacement.
• Heat energy is measured in calorie.
• S.I. unit of energy is joule (J) and C.G.S. unit is erg.
• 1 J = 10⁷ erg
• The bigger units of energy are watt hour and kilowatt hour.