Mechanics :- Work and Energy (points to remember)


1. Work done on an object by a constant force F is
W=Fx
where F is the magnitude of the force, Δx is the magnitude of the displacement,and F and Δx point in the same direction.
SI unit of work : joule ( J) newton.meter
2. Work done is a simple number that is it is a scalar quantity not a vector. So there is no direction associated with it. Energy and energy transfer are also scalar quantities.
3. The kinetic energy KE of an object of mass m moving with a speed v is
defined by
T=1/2(mv2)
SI unit: joule ( J) kg.m2/s2
4. The net work done on an object is equal to the change in the object’s
kinetic energy: Wtot=Tf-Ti=ΔT
where the change in the kinetic energy is due entirely to the object’s change in speed
5. A force is conservative if the work it does moving an object between two points is the same no matter what path is taken.
6. The gravitational potential energy of a system consisting of the Earth and an object of mass m near the Earth’s surface is given by
V=mgy
where g is the acceleration due to gravity and y is the vertical position of the mass with respect to the surface of the Earth (or some other reference point).

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