Physics Ch 8 MC

The graphs below show the magnitude of a force on a particle as the particle moves along the positive x axis from the origin to x=x1. The force is parallel to the x axis and is conservative. The maximum magnitude has the same value for all graphs. Rank the situations according to the change in potential energy associated with the force, least (or most negative) to greatest (or most positive).

2, 1, 3

Suppose that the fundamental dimensions are taken to be: force (F), velocity (V) and time (T). The dimensions of potential energy are then:

FVT

A ball is held at a height H above a floor. It is then released and falls to the floor. If air resistance can be ignored, which of the five graphs below correctly gives the mechanical energy E of the Earth-ball system as a function of the altitude y of the ball?

Graph E horizontal line

Two objects interact with each other and with no other objects. Initially object A has a speed of 5m/s and object B has a speed of 10m/s. In the course of their motion they return to their initial positions. Then A has a speed of 4m/s and B has a speed of 7m/s. We can conclude:

U=no change, Ktot=decreased, mech energy U+K=decreased, mechanical energy was decreased by nonconservative forces

A 2-kg block is thrown upward from a point 20m above Earth's surface. At what height above Earth's surface will the gravitational potential energy of the Earth-block system have increased by 500 J?

Ugi=mgd, h=(Ugi + J)/(mg)

A 6.0-kg block is released from rest 80m above the ground. When it has fallen 60m its kinetic energy is approximately:

Ui=mghi, Uf=mghf, Kf=Ui - Uf

A projectile of mass 0.50 kg is fired with an initial speed of 10m/s at an angle of 60deg above the horizontal. The potential energy of the projectile-Earth system (relative potential energy when the projectile is at ground level) is:

Voy=vsindeg, t=voy/g, h=(1/2)gt^2, U=mgh

A 2.2-kg block starts from rest on a rough inclined plane that makes an angle of 25deg with the horizontal. The coefficient of kinetic friction is 0.25. As the block goes 2.0m down the plane the mechanical energy of the Earth-block system changes by:

Wt=m*g, Wtx=Wtcosdeg, Ff=uk*Wty, W=-Ff*d

A good example of kinetic energy is provided by:

a tornado

No kinetic energy is possessed by:

an elevator standing at the fifth floor

Which one of the following five quantities CANNOT be used as a unit of potential energy?

gram·cm/s2

An example of a conservative force, a nonconservative force

gravity, friction

Only if a force on a particle is conservative:

is its work zero when the particle moves exactly once around any closed path

A body at rest in a system is capable of doing work if:

it is free to move in such a way as to decrease the potential energy of the system

A force on a particle is conservative if:

its work depends on the end points of every motion, not on the path between

For a block of mass m to slide without friction up the rise of height h shown, it must have a minimum kinetic energy of

mgh

The sum of the kinetic and potential energies of a system of objects is conserved

none of the above, as long as the only forces acting are conservative forces

A nonconservative force

none of the above, has work done around a closed path and depends on the path between

An elevator is rising at constant speed. Consider the following statements: I. the upward cable force is constant II. the kinetic energy of the elevator is constant III. the gravitational potential energy of the Earth-elevator system is constant IV. the acceleration of the elevator is zero V. the mechanical energy of the Earth-elevator system is constant

only I, II, and IV are true

The wound spring of a clock possesses:

potential but no kinetic energy

Two particles interact by conservative forces. In addition, an external force acts on each particle. They complete round trips, ending at the points where they started. Which of the following must have the same values at the beginning and end of this trip?

the potential energy of the two-particle system

A simple pendulum consists of a 2.0 kg mass attached to the string. It is released from rest at X as shown. Its speed at the lowest point Y is about:

v=sqrt(2gh)

A golf ball is struck by a golf club and falls on a green three meters above the tee. The potential energy of the Earth-ball system is greatest:

when the ball reaches the highest point in its flight