Exam 7: Work and Energy

You need to move a heavy crate by sliding it across a smooth floor-either by pushing it horizontally or by pulling it with a rope that makes a 30^o angle with the floor. If the coefficient of kinetic friction is 0.25, which way should you move the crate so that you do the least amount of work?

A box of mass m and a box of mass 4m are sliding with equal speeds along a level frictionless surface. Then they both slide up the same frictionless hill. Which rises to a greater height?

A heavy suitcase is carried by a porter down a flight of stairs. The work done on the suitcase by the porter is

At a water park, two slides with straight slopes, A and B, start and end at the same elevation. Slide A has a more gradual slope than B. Neglecting friction, your speed at the bottom of the slide is

An object is initially at rest on the ground. After a series of motions, it ends up at rest on a tower of height h. Which of the following statements is true?

As a 1.0-kg ball falls to the ground, its potential and kinetic energies are the same when the ball is 3.0 m above the ground. How fast is the ball moving just before the impact with the ground?

A box is in contact with a surface that makes an angle of 30^o with the horizontal. An applied horizontal force of 10.0 N allows the box to slide along the surface at a constant speed. When the box has moved 2.0 m along the surface, the net work done on it is

The work done to increase the speed of a car from 0.0 m/s to 10.0 m/s is 50.0 kJ. To increase the speed of the same car in the same conditions from 10.0 m/s to 20.0 m/s, the work done will be

A ball is dropped to the floor from a height h. It strikes the ground and briefly undergoes a change in shape before it bounces back. The height reached by the ball is

A heavy suitcase is carried by a porter down a flight of stairs. The net work done on the suitcase is

A girl runs up a flight of stairs at a constant speed v, and the gain in her potential gravitational energy is U. When she runs up the same stairs at half that speed, her mechanical energy is