WORK & WORK & ENERGYENERGY

AYUSHMAAN MAHESWARI

VISHAL TRIPATHI

ROHAN BAGHEL

ANUJ CHAUHAN

CLASS- 9 B

GROUP NO.- 3

G.L.T. SARASWATI BAL MANDIR

INDEX:-INDEX:-

1. WORK2. ENERGY

i. KINETIC ENERGYii. POTENTIAL ENERGY3. POWER

1. 1. WORK:-WORK:-Work is said to be done only when

a force act on an object which displaces it or which causes the object to move.

Work done = Force x Displacement

W = F swhere W= work done

F = forces = Displacement

In the SI system, the units of work are joules.

1 J = 1 Nm.E.g.-

W=F s

W=100 N*5m

W=500Nm

Energy:-Energy:-ENERGY is the capability of doing

work.An object having the capability to

do work is said to posses energy.The object which does the work

loses energy and the object on which the work is done gains energy.

Any object that possesses energy can do work.

The unit of energy is the same as that of work. i.e. joule (J)

Different forms of ENERGY.-1.Mechanical Energy

(Potential Energy + Kinetic Energy)

2.Heat Energy3.Chemical Energy4.Electrical Energy5.Light Energy

1. 1. Kinetic Energy:-Kinetic Energy:-The kinetic energy of an object

is the energy which it possesses due to its motion.

We define the kinetic energy:-KE = W = F x d= m a h=1/2

mv2

• If the net work is positive, the kinetic energy increases.

• If the net work is negative, the kinetic energy decreases.

e.g.-Find the kinetic energy of an 4 Kg object

moving at 5m/s.KE = 1/2 mv2

KE = ½ (4Kg)(5m/s) 2

KE = 50 Kg m 2 /s 2

KE = 50 J

2. 2. POTENTIAL ENERGY:-POTENTIAL ENERGY:-Potential energy is energy that is

stored within a system.This force is often called a restoring

force.  PE = W = F x d = m a h

Familiar examples of potential energy:

• A wound-up spring

• A stretched elastic band

• An object at some height above the ground

In raising a mass m to a height h, the work done by the external force is

Therefore define the gravitational potential energy:

The energy of motionKE = W = F x d = m a h=1/2 mv2

Find the kinetic energy of an 4 Kg object moving at 5m/s.

KE = 1/2 mv2

KE = ½ (4Kg)(5m/s) 2

KE = 50 Kg m 2 /s 2

KE = 50 J

Potential energy can also be stored in a spring when it is compressed; the figure below shows potential energy yielding kinetic energy.

The force required to compress or stretch a spring is:

where k is called the spring constant, and needs to be measured for each spring.

If there are no non-conservative forces, the sum of the changes in the kinetic energy and in the potential energy is zero – the kinetic and potential energy changes are equal but opposite in sign.

This allows us to define the total mechanical energy:

Potential Energy is maximum at the maximum HEIGHT

Law of conservation of Law of conservation of energy energy Energy cannot

be created or destroyed; hence energy can not disappear.

POWER:-POWER:-Power is the rate that we use

energy.Power = Work or Energy / TimeP = W/t = F x d/t = F vThe units for power :

◦J/s◦Kg m2 / s2 /s◦N m / s

In the SI system, the units of power are watts:

A 5 Kg Cart is pushed by a 30 N force against friction for a distance of 10m in 5 seconds. Determine the Power needed to move the cart.

P = F x d / tP = 30 N (10 m) / 5 sP = 60 N m /sP = 60 watts

Power is also needed for acceleration and for moving against the force of gravity.

The average power can be written in terms of the force and the average velocity:

THANK YOUTHANK YOU