presentation mechanical energy

8/6/2019 Presentation Mechanical Energy

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Mechanical Energy

(for IX standard)



What is ENERGY?

An object having capability to do work is

said to possess energy . The object which

does the work, loses energy and the objecton which the work is done, gains energy.

Energy gainEnergy loss



UNIT of Energy The energy is the work possessed by an

object or measured in terms of its capacity

of doing work. The unit of energy is,therefore the same as that of work, that is,

joule(J).

Larger unit of energy

1 kJ =1000 J



Types of Energy Chemical energy

Light energy

Sound energy

Electric energy

Mechanical energy

Nuclear energy



MECHANICAL ENERGY

MECHANICAL ENERGY

POTENTIAL ENERGYKINETIC ENERGY

It is a combination of kinetic and potential

energy resulting from the force of gravity

or the movement of the object.



K INETIC ENERGY

Kinetic energy is the energy possessed by

an object due to its motion. The kinetic

energy is the energy of an objectincreases with its speed.



FORMULA

The kinetic energy possessed by an object

of mass m and moving with uniform

velocity, v is

K.E. = ½ mv2

V

m



Solved Problem

Q. An object of mass 15 kg is moving with

unifor m velocity of 4 m/s. What is the kinetic

energy possessed by the object ?

Solution : Mass of the object m = 15 kg,

Velocity of the object, v = 4 m/s,

Using equation

K.E. = ½ mv2

= ½ x 15 x 4 x 4

= 120 J



POTENTIAL ENERGY

h

The gravitational energy or potential energy

of an object at a point above the ground is

defined as the work done in raising i t from

the ground t o that point against gravi t y



FORMULA

P.E. = mgh

h

Potential energy is equal to the work done onthe object, to displace it from ground to height

h.

m



1. The potential energy of an object at a

height depends on the ground or zero level

choose.

IMPORTANT POINTS

Ground level

Zero level

h h1



2.The work done by gravity or potential

energy depends on the difference in verticalheights of the initial and final position of

object and not on the path along which the

object is moved.

hPath 1

P.E. =m

gh

hPath 2

P.E. = mgh



Solved Problem

Q. Find the energy possessed by an objectof mass 10 kg when it is at a height of 6 m above the ground.

Given g = 9.8 m/s2

Solution : Mass of the object m = 10 kg,

Displacement (height), h = 6 m, and

Acceleration due to gravity, g = 9.8 m/s2.

Using equation P.E. = mgh

= 10 x 9.8 x 6

= 588 J



MECHANICAL ENERGY

MECHANICAL ENERGY = KINETIC ENERGY +

POTENTIAL ENERGY

KINETIC ENERGY = ½ mv2

POTENTIAL ENERGY = mgh

½ mv2

MECHANICAL ENERGY =

mgh



Practice Question

1.The kinetic energy of an object of mass m moving with avelocity of 5 m/s is 25 J. What will be its kinetic energywhen its velocity is doubled ? What will be its kineticenergy when its velocity is increased three times?

2. An object of mass 40 kg is raised to height of 5 m

above the ground. What is its potential energy? 3.What is the work to be done to increase the velocity of a

car from 30 km/hr to 60 km/hr if the mass of the car is1500 kg?

4. An object of mass 12 kg is at a certain height above theground. If the potential energy of the object is 480 J. Findthe height at which the object is with respect to ground,given g = 10 m/s2.

presentation mechanical energy

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