## Springs

^Springs 1. Spring force does -ve work when we expand or stretch & +ve work when the spring force restores itself from extended or stretched positions. 2.Spring store energy called elastic potential energy whether expanded or stretched from relaxed state. 3.If a block of mass ‘m’ is released on a spring of stiffness constant ‘k’ […]

## Work energy theorem

^Work energy theorem Total work done by all the forces acting on a system between any two points is equal to change of kinetic energy between those two points.          Here all forces means real or pseudo, conservative or non, internal or external.

## Conservation of mechanical energy

^Conservation of mechanical energy K + U = E = constant                                  or  – (UB – UA) = + (KB – KA)In a conservative field loss of potential energy between any two points is always equal to gain of KE […]

## Work by a conservative force

^Work by a conservative force Work done by a conservative force in moving a body from one point say ‘A’ to other point say ‘B’  is always equal to loss of potential energy between same points i.e., Here the negative sign implies that a conservative force is always directed in the direction of decreasing potential […]

## ^Potential energy

^Potential energy  Potential energy is defined only for conservative forces. Gravitation, electromagnetic, spring force all are conservative. Friction is non conservative. Usually a point at infinity is assigned zero value i.e. U∞ = 0 Potential energy can be + ve, -ve or zero. Generally –ve potential energy indicates attractive forces & +ve indicates repulsive forces.

## ^Kinetic energy

^Kinetic energy  Kinetic means motion. A mass ‘m’ moving at As both m & v2 are + ve & scalar, thus the KE of a body is always a +ve scalar quantity. Where as linear momentum is vector and always directed in the direction of velocity. KE of a system of particles is the sum […]

## ^Work to pull a chain

^Work to pull a chain A chain is held on a frictionless table with 1/n of its length hanging over the edge. If the chain has a length L and a mass M. Work required to pull the hanging part back on the table is,

## ^Calculating work from F – x graph

^Calculating work from F – x graph is read as work done by a force ‘Fx’ in moving an object form point A to point B is equal to area under F – x graph bounded with the displacement – axis under position limits of the point A & B. Conventionally upward areas are +ve […]

## ^Examples of zero,  +ve & -ve work

^Examples of zero,  +ve & -ve work Zero work means either no displacement of system no net change in the KE of the system. Few examples of zero work are If there is no motion, no work has been done no matter how much force is applied. A static person e.g.  a gate keeper does […]

## ^Sign of work

^Sign of work Sign of work depends on sign of cosθ. As cosθ can be 0, +ve or – ve (recall –1 ≤ cosθ ≤ +1), hence the work done by a force also can be 0, + ve or – ve depending upon the angle between the force and the displacement. Work done by […]

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