WORK ENERGY THEOREM

STATEMENT-1: Work done by the net force acting on a particle is equal to the change in its kinetic energy. STATEMENT-2: Change in potential energy is always equal to the work done by external forces. STATEMENT-3: Work energy theorem is not applicable, if the work is done by the non-conservative forces

Work Power And Energy - Problems On Energy

Work Power And Energy - Potential Energy

In picking upan object from the floor and putting it on a table, we do work. However, the initial and final values ofthe object's kinetic energy are zero. Is there a violation of the work energy theorem here ? Explain why or why not.

You are reshelving books in a library. You lift a book from the floor to the top shelf. The kinetic energy of the book on the floor was zero and the kinetic energy of the book on the top shelf is zero, so no change occurs in the kinetic energy even though you did some work in lifting the books. Is the work-kinetic energy theorem violated?

According to work energy theorem or work energy principle, work done by net force in displacing a body is always equal to change in K.E. of the body. Similarly , if some work is drawn from the body, K.E. of the body decreases by the same amount. In either process, we assume that potential energy of the body does not change. Read the above passage and answer the following question: (i) A car weighing 500 kg is running at a speed of 72 km//h . In how much distance will it stope by applying a braking force of 4000N? (ii) What are the implication of this theorem in day to day life ?

A point charge q_(0) is moved slowly from the centre of a ring R, ( that is carrying a charge q) to a distance x from its centre along its axis. What is the work done by the external agent in this process ? Strategy : According to work energy theorem, if there is no change in kinetic energy, we have W_(ext)+ W_(E ) = 0 implies W _(ext) = - W_(E ) = - q_(0)(V_(A)-V_(B))

A mass of 0.675 kg on a frictionless table is attached to a string which passes through a hole in the table at the centre. If the radius of the circle in which the mass rotates, is 5 m when its speed is 10 ms^(-1) , find the tension of the string. It is found that on drawing down the string by 0.2 m, the tension is increased 4.63 times. Calculate the work done by the string on the revolving mass during the reduction of the radius. [Hint : Apply work-energy theorem to find work done by the force]

(i) The cause of increases in kinetic energy when a man starts running without his feet slipping on ground is asked to two students. Their answers are– Harshit: Cause of increase in kinetic energy is work done by friction force. Without friction the man cannot run. Akanksha: Cause of increase in kinetic energy is work done by internal (muscle) forces of the body. Who is right? (ii) An inextensible rope is hanging from a tree. A monkey, having mass m, climbs to a height h grabbing the rope tightly. The monkey starts from rest and ends up hanging motionlessly on the rope at height h. (a) How much work is done by gravity on the monkey? (b) How much work is done by the rope on the monkey? (c) Using work – energy theorem, explain the increase in mechanical energy of the monkey.

A block of mass 2kg slides on a frictionless table with with a speed of 10 ms^(-1) . Directly in front of it and moving in the same direction is a block of mass 5 kg moving at 3 ms^(-1) . A massless spring with force constant k = 1120 Nm^(-1) is attached to its back (the side facing 2 kg mass) When the blocks collide, what is the maximum compression of the spring ? [Hint : Apply 'work energy' theorem to the system of block and principle of conservation of momentum]