Work, Energy, and Power Paper 1 (1-16)

C. 2EK.

A body of mass m and speed v has kinetic energy EK. A second body of mass moves at speed 2v. The kinetic energy of this second body is A. B. EK. C. 2EK. D. 4EK.

D. fs.

A box of mass m is moved horizontally against a constant frictional force f through a distance s at constant speed v. The work done on the box is A. 0. B. mgs. C. mv2. D. fs.

D.

A machine lifts an object of weight 1.5 × 103 N to a height of 10 m. The machine has an overall efficiency of 20%. The work done by the machine in raising the object is A. 3.0 × 103 J. B. 1.2 × 104 J. C. 1.8 × 104 J. D. 7.5 × 104 J.

A. zero

A stone of mass m is attached to a string and moves round in a horizontal circle of radius R at constant speed V. The work done by the pull of the string on the stone in one complete revolution is A. zero. B. 2πmV^2. C. 2πmV^2/R D. 2πmV/R

A

An amount Q of energy is supplied to a machine. The machine does useful work W and an amount R of energy is wasted, as illustrated below. Which one of the following is a correct expression for the efficiency of the machine? A. W/Q B. R/Q C. W+R/Q D. W-R/Q

B. 3.0 m s-1.

An electric motor is used to raise a weight of 2.0 N. When connected to a 4.0 V supply, the current in the motor is 1.5 A. Assuming no energy losses, the best estimate for the maximum steady speed at which the weight can be raised is A. 0.3 m s-1. B. 3.0 m s-1. C. 9.0 m s-1. D. 12.0 m s-1.

C. 20 kN.

An electric train develops a power of 1.0 MW when travelling at a constant speed of 50 ms-1. The net resistive force acting on the train is A. 50 MN. B. 200 kN. C. 20 kN. D. 200 N.

B.

An engine takes in an amount E of thermal energy and, as a result, does an amount W of useful work. An amount H of thermal energy is ejected. The law of conservation of energy and the efficiency of the engine are given by which of the following?

A.

An object of mass m1 has a kinetic energy K1. Another object of mass m2 has a kinetic energy K2. If the momentum of both objects is the same, the ratio is equal to

C.

The diagram below represents energy transfers in an engine. The efficiency of the engine is given by the expression

D. VQRT

The diagram below shows the variation with displacement x of the force F acting on an object in the direction of the displacement. Which area represents the work done by the force when the displacement changes from x1 to x2? A. QRS B. WPRT C. WPQV D. VQRT

C. 5 × 10-2J

The graph below shows the variation with displacement d of the force F applied by a spring on a cart. The work done by the force in moving the cart through a distance of 2 cm is A. 10 × 10-2J. B. 7 × 10-2J. C. 5 × 10-2J. D. 2.5 × 10-2J.

C. Fd cos θ

The point of action of a constant force F is displaced a distance d. The angle between the force and the direction of the displacement is θ, as shown below. Which one of the following is the correct expression for the work done by the force? A. Fd B. Fd sin θ C. Fd cos θ D. Fd tan θ

B.

The variation with time of the vertical speed of a ball falling in air is shown below. During the time from 0 to T, the ball gains kinetic energy and loses gravitational potential energy ΔEp. Which of the following statements is true? A. ΔEp is equal to the gain in kinetic energy. B. ΔEp is greater than the gain in kinetic energy. C. ΔEp is equal to the work done against air resistance. D. ΔEp is less than the work done against air resistance.

A. Some ice and water as the ice melts at constant temperature.

Which of the following involves a change in the total energy of the objects? A. Some ice and water as the ice melts at constant temperature. B. An electron accelerated by a magnetic field. C. A satellite in a circular orbit round the Earth. D. A stone falling in a vacuum towards the Earth's surface.

B. Energy is a measure of the ability to do work.

Which one of the following is a true statement about energy? A. Energy is destroyed due to frictional forces. B. Energy is a measure of the ability to do work. C. More energy is available when there is a larger power. D. Energy and power both measure the same quantity.