Work, Energy, and Power Physics - Work, Energy, and Power

A mass of 0.5kg moving with a speed of 1.5ms^-1 on a horizontal smooth surface, collides with a nearly weightless spring of spring constant k = 50N/ m^-1

The maximum compression of the spring would be:

A body of mass 2kg makes an elastic collision with another body at rest and comes to rest. The mass of the second body which collides with the first body is:

Which one of the following energies cannot be possessed by a body at rest?

Which one of the following possesses potential energy?

A ball is projected upwards. As it rises, there is increase in its:

State if the following statements is true or false. Give reasons for your answer:
Total energy of a system is always conserved, no matter what internal and external forces on the body are present.

State if the following statements is true or false. Give reasons for your answer:
In an inelastic collision, the final kinetic energy is always less than the initial kinetic energy of the system.

State if the following statements is true or false. Give reasons for your answer:
In an elastic collision of two bodies, the momentum and energy of each body is conserved.

State if the following statements is true or false. Give reasons for your answer:
Work done in the motion of a body over a closed loop is zero for every force in nature.

A body of mass 2kg initially at rest moves under the action of an applied horizontal force of 7N on a table with coefficient of kinetic friction = 0.1. Compute the:
Work done by friction in 10 s.

State if the following statements is true or false. Give reasons for your answer:
In an elastic collision of two bodies, the momentum and energy of each body is conserved.

State if the following statements is true or false. Give reasons for your answer:
Work done in the motion of a body over a closed loop is zero for every force in nature.

A bolt of mass 0.3kg falls from the ceiling of an elevator moving down with an uniform speed of 7ms^-1. It hits the floor of the elevator (length of the elevator = 3m) and does not rebound. What is the heat produced by the impact? Would your answer be different if the elevator were stationary?

A 1kg block situated on a rough incline is connected to a spring of spring constant 100Nm^-1 as shown in. The block is released from rest with the spring in the unstretched position. The block moves 10cm down the incline before coming to rest. Find the coefficient of friction between the block and the incline. Assume that the spring has a negligible mass and the pulley is frictionless.

A cyclist comes to a skidding stop in 10 m. During this process, the force on the cycle due to the road is 200 N and is directly opposed to the motion. (a) How much work does the road do on the cycle ? (b) How much work does the cycle do on the road ?

Which of the following potential energy curves in cannot possibly describe the elastic collision of two billiard balls? Here r is the distance between centres of the balls.

A trolley of mass 300kg carrying a sandbag of 25kg is moving uniformly with a speed of 27km/h on a frictionless track. After a while, sand starts leaking out of a hole on the floor of the trolley at the rate of 0.05 kgs^-1. What is the speed of the trolley after the entire sand bag is empty?

Consider the decay of a free neutron at rest: n → p + e^- Show that the two-body decay of this type must necessarily give an electron of fixed energy and, therefore, cannot account for the observed continuous energy distribution in the β-decay of a neutron or a nucleus.

[Note: The simple result of this exercise was one among the several arguments advanced by W. Pauli to predict the existence of a third particle in the decay products of β-decay. This particle is known as neutrino. We now know that it is a particle of intrinsic spin ½ (like e^-, p or n), but is neutral, and either massless or having an extremely small mass (compared to the mass of electron) and which interacts very weakly with matter. The correct decay process of neutron is: n → p + e^- + v]

The US athlete Florence Griffith-Joyner won the 100m sprint gold medal at Seol Olympic 1988 setting a new Olympic record of 10.54s. Assume that she achieved her maximum speed in a very short-time and then ran the race with that speed till she crossed the line. Take her mass to be 50kg.

1. Calculate the kinetic energy of Griffith-Joyner at her full speed.
2. Assuming that the track, the wind etc. offered an average resistance of one tenth of her weight, calculate the work done by the resistance during the run.
3. What power GriffithJoyner had to exert to maintain uniform speed?

Consider a gravity-free hall in which an experimenter of mass 50kg is resting on a 5kg pillow, 8ft above the floor of the hall. He pushes the pillow down so that it starts falling at a speed of 8ft/s. The pillow makes a perfectly elastic collision with the floor, rebounds and reaches the experimenter's head. Find the time elapsed in the process.

A collision experiment is done on a horizontal table kept in an elevator. Do you expect a change in the results if the elevator is accelerated up or down because of the noninertial character of the frame?

When you push your bicycle up on an incline the potential energy of the bicyle and yourself increases. Where does this energy come from?

A person trying to lose weight (dieter) lifts a 10kg mass, one thousand times, to a height of 0.5m each time. Assume that the potential energy lost each time she lowers the mass is dissipated.

1. How much work does she do against the gravitational force?
2. Fat supplies 3.8 × 107J of energy per kilogram which is converted to mechanical energy with a 20% efficiency rate. How much fat will the dieter use up?

A bullet of mass 0.012kg and horizontal speed 70ms^-1 strikes a block of wood of mass 0.4kg and instantly comes to rest with respect to the block. The block is suspended from the ceiling by means of thin wires. Calculate the height to which the block rises. Also, estimate the amount of heat produced in the block.

Given in are examples of some potential energy functions in one dimension. The total energy of the particle is indicated by a cross on the ordinate axis. In each case, specify the regions, if any, in which the particle cannot be found for the given energy. Also, indicate the minimum total energy the particle must have in each case. Think of simple physical contexts for which these potential energy shapes are relevan.

Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed V. If the collision is elastic, which of the following is a possible result after collision?