Exam 7: Work and Kinetic Energy

A block of mass m is pushed against a spring of spring constant k. The spring is compressed by a distance d, the block is then released. It is launched by the spring along a horizontal frictionless surface with a final speed v. A second block, this one having mass 4m is pushed against the same spring and released, gaining a final speed 2v. By what distance was the spring compressed in the second case?

Kinetic energy is a scalar quantity.

John's mass is half the mass of Jill. They both start walking and John moves twice as fast as Jill. What is the ratio of the kinetic energy of Jill to the kinetic energy of John?

As plant engineer, Donna purchases an electrical motor which has an output of 1500. hp. If it requires 1.20 Megawatts of electricity, what is the efficiency of the motor?

A spring with a spring constant of 2500 N/m. is stretched 4.00 cm. What is the work required to stretch the spring?

An ordinary light bulb consumes 60 W of power. Through what height could a 1000-N object be lifted expending the same amount of power for 6 hours?

The ratio of the final kinetic energy to the initial kinetic energy of an object is one half. If the initial velocity of the object is 10 m/s, what is the final velocity?

FIGURE 7-2 Three applied forces, F₁ = 20.0 N, F₂ = 40.0 N, and F₃ = 10.0 N act on an object with a mass of 2.00 kg which can move along an inclined plane as shown in the figure. The questions refer to the instant when the object has moved 0.600 m along the surface of the inclined plane in the upward direction. Neglect friction and use g = 10.0 m/s². -Refer to Figure 7-2. What is the amount of work done by the force F₃ as the object moves up the inclined plane?

FIGURE 7-3 -An object of mass = 2 kg is pulled by a constant force F = 4 N for a horizontal distance of 2 m. (Refer to Figure 7-3.) What is the work done along the +x-axis? Neglect friction.

A man drags a 130-kg object down an inclined plane at a speed of 1.40 m/s. The coefficient of friction between the object and the inclined plane is 0.800 and the angle of inclination with the horizontal is 23.0°. What is the amount of power this man expends in dragging this object? Use g = 10.0 m/s².

The work required to stretch a spring changes linearly with the amount of stretch.

A ball is thrown upward with a speed and direction such that it reaches a maximum height of 16.0 m above the point it was released. At its maximum height it has a speed of 18.0 m/s. With what speed was the ball released?

Which object has larger kinetic energy: a 500-kg object moving with a speed of 40 m/s or 1000-kg object moving at 20 m/s?

A car starts from rest and after 6.0 seconds it has a kinetic energy of 60,000 J. How much horsepower is needed for the car to acquire this kinetic energy?

A constant force of 20 N is applied to an object of mass 8.0 kg at an angle of 25° with the horizontal. What is the work done by this force on the object if it causes a displacement of 2.0 m along the horizontal direction?

A 20-N horizontal force pushes an object along a rough floor so that the object moves with a constant velocity of 6.0 m/s. How much power does this force deliver to the object?

State the work-energy theorem.

A 20.0-N weight slides down a rough inclined plane which makes an angle of 30.0° with the horizontal. The weight starts from rest and gains a speed of 15.0 m/s after sliding 150 m. How much work is done against friction? Use g = 10 m/s².

Kinetic energy is proportional to speed.

Can work be done on a system if there is no motion?