Ch. 7 physics PLR

When a flea (mm = 450 μgμg) is jumping up, it extends its legs 0.5 mmmm and reaches a speed of 1 m/sm/s in that time. How high can this flea jump? Ignore air drag and use gg = 10 m/s2m/s2.

0.050 m

Consider the video demonstration that you just watched. Which of the following changes could potentially allow the ball on the straight inclined (yellow) track to win? Ignore air resistance.

Increase the tilt of the yellow track. If the yellow track were tilted steeply enough, its ball could win. How might you go about calculating the necessary change in tilt?

Which of the following statements is/are true?

Mechanical energy can be dissipated to nonmechanical forms of energy. The total mechanical energy of a system is constant only if conservative forces act.

Two identical balls are thrown vertically upward. The second ball is thrown with an initial speed that is twice that of the first ball. How does the maximum height of the two balls compare?

The maximum height of the second ball is four times that of the first ball.

A person applies a 50 N force on a crate, causing it to move horizontally at a constant speed through a distance of 10 m. What is the net work done on the crate?

The net work done on the crate is zero joules.

If the net work done on an object is positive, what can you conclude about the object's motion?

The object is speeding up.

If the net work done on an object is zero, what can you determine about the object's kinetic energy?

The object's kinetic energy remains the same.

Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height?

The two objects rise to the same height.

A motorcycle drives up a steeply inclined ramp. The work done on the motorcycle by the Earth's gravitational force is ____.

negative. When an object's displacement has a component in a direction opposite that of a given force, that force does negative work on the object.

During a certain time interval, the net work done on an object is zero joules. We can be certain that ____.

the object's final speed was the same as its initial speed. When the net work done on an object is zero, there is no overall change in the object's kinetic energy.

Two identical cars are driving in opposite directions at the same speed. Their kinetic energies have ____.

the same magnitude and sign. The kinetic energy of a moving object is always positive, regardless of the direction it is moving in, or the coordinate system used.

Which of the following statements is/are true?

The work done by a nonconservative force depends on the path taken. A potential energy function can be specified for a conservative force. A conservative force permits a two-way conversion between kinetic and potential energies.

A graph depicts force versus position. What represents the work done by the force over the given displacement?

The work done is equal to the area under the curve.

An object weighing 20 N moves horizontally toward the right a distance of 5.0 m. What is the work done on the object by the force of gravity?

The work done on the object by the force of gravity is zero joules.

A ball is thrown straight upward. How does the sign of the work done by gravity while the ball is traveling upward compare with the sign of the work done by gravity while the ball is traveling downward?

Work done by gravity is negative while the ball is traveling upward and positive while the ball is traveling downward.