Chapter 7 Physics 105
Wp=((1/2mv0^2)/x1)(x2-x1)+1/2mv1^2
After the box comes to rest at position x1, a person starts pushing the box, giving it a speed v1.When the box reaches position x2(where x2>x1), how much work Wp has the person done on the box?Assume that the box reaches x2after the person has accelerated it from rest to speed v1. Express the work in terms of m, v0, x1, x2, and v1.
Wd/Wp=1
Consider lifting a box of mass mto a height h using two different methods: lifting the box directly or lifting the box using a pulley (as in the previous part). What is Wd/Wp, the ratio of the work done lifting the box directly to the work done lifting the box with a pulley? Express the ratio numerically.
F=1/2mg
Once you have pulled hard enough to start the box moving upward, what is the magnitude F of the upward force you must apply to the rope to start raising the box with constant velocity? Express the magnitude of the force in terms of m, the mass of the box.
change/potential
Rather than ascribing the increased kinetic energy of the stone to the work of gravity, we now (when using potential energy rather than work-energy) say that the increased kinetic energy comes from the ______ of the _______ energy.
It will take less time to return to the point from which it was released.
Suppose our experimenter repeats his experiment on a planet more massive than Earth, where the acceleration due to gravity is g=30 m/s2. When he releases the ball from chin height without giving it a push, how will the ball's behavior differ from its behavior on Earth? Ignore friction and air resistance. (Select all that apply.)
Ff=m(v0)^2/2x1
The box leaves position x=0 with speed v0. The box is slowed by a constant frictional force until it comes to rest at position x=x1.Find Ff, the magnitude of the average frictional force that acts on the box. (Since you don't know the coefficient of friction, don't include it in your answer.) Express the frictional force in terms of m, v0, and x1.
distance/kinetic
The work-energy theorem states that a force acting on a particle as it moves over a ______ changes the ______ energy of the particle if the force has a component parallel to the motion.
sum/conserved
This process happens in such a way that total mechanical energy, equal to the ______ of the kinetic and potential energies, is _______.
distance
To calculate the change in energy, you must know the force as a function of _______. The work done by the force causes the energy change.
force/kinetic
To illustrate the work-energy concept, consider the case of a stone falling from xi to xf under the influence of gravity. Using the work-energy concept, we say that work is done by the gravitational _____, resulting in an increase of the ______ energy of the stone.
The maximum height of the second ball is four times that of the first ball.
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 two objects rise to the same height.
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?
A conservative force permits a two-way conversion between kinetic between kinetic and potential energies. A potential energy function can be specified for a conservative force. The work done by a nonconservative force depends on the path taken.
Which of the following statements is/are true?
Mechanical energy can be displayed to nonmechanical forms of energy. The total mechanical energy of a system is constant only if conservative forces act.
Which of the following statements is/are true?