• Energy is a scalar quantity.

• It was first hypothesized by Newton to express kinetic and potential energies.

• We cannot observe energy directly, but we can measure it using indirect methods and analyze its value.

• Energy may be in different forms, such as potential, kinetic, magnetic or electrical.

Potential energy of a system is by virtue of its location with respect to gravitational field. If an object has a mass m, located at elevation h, and acceleration due to gravity is g, then the potential energy is, EPE = mgh (1.1)

Kinetic energy of an object is due to its velocity. If an object is moving with a velocity u, and it has mass m, then its kinetic energy is,

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If the magnitude of all other energy forms are small in comparison with the kinetic, potential and internal energies, then ETOTAL = EKE + EPE + Ei (1.4)

PROBLEM 1.

A small object of mass m=234g slides along a track with elevated ends and a central flat part. The flat part has a length L=2.16m. The curved portions the tracks are frictionless; but it travelling the flat part, the object loses 688 mJ of mechanical energy, due to friction. The object is released at point A, which is height h= 1.05 m above the flat part of the track. Where does the object finally come to rest?

Concept:

The potential energy U is defined as:

U=mgh

Here, m is the mass of the body, g is the free fall acceleration and h is the fall of height.

Solution:

To find the potential energy of the object at the point A, substitute 234g for mass of the object m, 9.81 m/s2 for free fall acceleration g and 1.05 m for height h in the equation