WORK, ENERGY AND POWER

PRESENTED BY:

AROSEK PADHI - CL – XI

A SIMPLE QUESTION.ARE THEY WORKING

Is this guy working ? Yes he seems to push the wall. But No, he is not working. To know why he’s not working let’s know a few things about WORK and WORK DONE

This guy is working !! Well,…He’s going to office to WORK as it may seem.

WORK

IF A FORCE IS APPLIED ON A BODY IN A DIFFERENT DIRECTION OF DISPLACEMENT OF THE BODY AND THE

BODY UNDERGOES A DIAPLACEMENT IN THE POSITIVE X – DIRECTION, THE WORK DONE BY THE FORCE IS

DEFINED AS THE PRODUCT OF COMPONENT OF THE FORCE IN THE DIRECTION OF THE DISPALCEMENT AND

THE MAGNITUDE OF THIS DISPLACEMENT

W = (FcosƟ)d = .

IN TERMS OF UNITS…..

WORK IS SAID TO BE 1 JOULE, WHEN A FORCE OF ONE NEWTON ACTUALLY MOVES A BODY THROUGH A DISTANCE OF ONE METRE IN THE DIRECTION OF THE APPLIED FORCE.

WORK IS SAID TO BE ONE kg-m, WHEN A FORCE OF 1 kgf (or 1 kg wt) MOVES A BODY THROUGH A DISTANCE OF 1m IN THE DIRECTION OF THE APPLIED FORCE. WORK IS SAID TO BE ONE g-cm, WHEN

A FORCE OF 1 gf MOVES A BODY THROUGH A DISTANCE OF 1 cm IN THE DIRECTION OF THE APPLIED FORCE

WORK IS SAID TO BE 1 ERG, WHEN A FORCE OF ONE DYNE ACTUALLY MOVES A BODY THROUGH A DISTANCE OF ONE CENTIMETRE IN TE DIRECTION OF THE APPLIED FORCE.

KINETIC ENERGY

IT IS A SCALAR QUANTITY. IT IS MEASURE OF THE

WORK AN OBJECT CAN DO BECAUSE OF ITS MOTION.

DERIVATION OF KINETIC ENERGY

BY CALCULUS METHOD

RELATION BETWEEN KINETIC ENERGY AND LINEAR

MOMENTUM

STOPPING DISTANCEWHEN A BODY SLIDE d DISTANCE ON AROUGH HORIZONTAL SURFACE WITH VELOCITY V, ITS

STOPPING DISTANCE S GIVEN BY:

THE WORK-ENERGY

THEOREM

WORK ENERGY THEOREM IS AN INTEGRAL FORM OF NEWTON’S 2ND LAW. IT DOES NOT, IN GENERAL

INCORPORATE THE COMPLETE DYNAMICAL INFORMATION OF 2ND LAW, WHICH IS A RELATION BETWEEN FORCE AND

ACCERELATION AT ANY TIME. THE W-E THEOREM INVOLVES AN INTEGRAL OVER AN INTERVAL OF TIME. THE TEMPORAL (TIME) INFORMATION CONTAINED IN THE 2ND

LAW IS INTEGRATED OVER AND IS NOT AVAILABLE EXPLICITLY.

THE CONSERVATION OF MECHANICAL ENERGY

THE TOTAL MECHANICAL ENERGY OF A SYSTEMIS CONSERVED IF THE FORCES DOING WORK ON OT, ARE CONSERVATIVE.

A FORCE IS CONSERVATIVE IF IT CAN BE DERIVED FROM A SCALAR QUANTITY.

THE WORK DONE BY THE CONSERVATIVE FORCE DEPENDS ONLY ON THE END POINTS

WORK DONE BY THE CONSERVATIVE FORCE IN A CLOSED PATH IS ZERO. THIS IS APPARENT AS Xi = Xf

PROPERTIES OF CONSERVATIVE AND NON- CONSERVATIVE FORCES

MOTION IN A

VERTICAL CIRCLE

POTENTIAL ENERGY CURVE AND EQUILIBRIUM SYSTEM

AN OBJECT IS SAID TO BE IN STABLE EQUILIBRIUM, IF ON SLIGHT

DISPLACEMENT FROM EQUILIBRIUM POSITION IT HAS TENDENCY TO COME

BACK TO ITS ORIGINAL POSITION. IN THIS CASE OF STABLE EQUILIBRIUM THE POTENTIAL ENERGY IS MINIMUM.

AN OBJECT IS SAID TO BE IN UNSTABLE EQUILIBRIUM, IT ON SLIGHT DISPLACEMENT FROM EQUILIBRIUM POSITION IT MOVES IN THE DIRECTION OF DISPLACEMENT. THE POTENTIAL ENERGY IS MAXIMUM IN EQUILLIBRIUM STATE.

POWER IS DEFINED AS THE TIME RATE AT WHICH WORK IS DONE OR ENERGY IS

TRANSFERRED. THE AVERAGE POWER OF A FORCE IS DEFINED AS THE RATIO OF THE

WORK, W TO THE TOAL TIME t TAKEN

P =

COLLISIONTYPES:- (on the basis of dimensions)

1D COLLISION2D COLLISION

TYPES:-

ELASTICINELASTICSEM-IELASTIC

EXPRESSIONS FOR VELOCITIES OF THE BODIES AFTER THE

1D ELASTIC COLLISION

2D ELASTIC COLLISION

Hence,ɸ + Ɵ = 900

PERFECTLY INELASTIC COLLISION

IF THE MAXIMUM DEORMATION IN THE COLLIDING BODIES DURING THE

DEFORMING PERIOD IS NOT RECOVERED AT ALL, THE COLISION IS SAID TO BE

PERFECTLY INELASTIC

NOTE:IF WE PUT e = 1, IN THE ABOVE EQUATION, THEN WE WILL GET THE VELOCITIES OF THE BODIES

AFTER COLLISION IN ELASTIC CONDITION.