Work, Energy and PowerNEET Physics · Class 11 · NCERT Chapter 5

You can expect 3 to 5 questions from Work, Energy and Power in NEET 2027. The chapter has the highest PYQ frequency in Class 11 Physics. Work-energy theorem, spring energy, conservation of energy, power and 1D collisions are tested almost every year.

Energy methods often solve problems that look impossible by force methods. Once you have the work-energy theorem, you can answer questions about the speed of a body at a given point without ever computing the force on it. NEET examiners love problems that mix springs, inclined planes, friction and circular motion — all easier with energy.

The net work done on a body equals its change in kinetic energy. In symbols, W_net = (1/2)mv squared minus (1/2)mu squared. This single statement replaces a long sequence of force and acceleration calculations.

A spring stretched (or compressed) from its natural length by x stores potential energy U = (1/2)kx squared, where k is the spring constant. Note the square: doubling the extension quadruples the stored energy.

Average power equals total work divided by total time, P_avg = W over t. Instantaneous power is the rate at that instant, P = F dot v. They are equal when the force and speed are constant; they differ when either changes.

For one body of mass m1 with velocity u colliding with another mass m2 at rest, the kinetic energy lost is (m1 m2 over m1 plus m2) times (u squared over 2). Maximum loss happens when the masses are equal — half the original KE is converted to heat or deformation.

For a body moving on the inside of a vertical loop of radius r, the minimum speed at the top is the square root of (g r). At this speed, gravity alone provides the centripetal force; the string or track tension is zero. Below this speed, the body falls off the loop.