Ch 12 study guide
Energy is transferred as ____________________ when mechanical energy decreases and temperature increases.
Heat
The brakes on a car exert a frictional force of 6000 N in getting the car to stop. If the work done by the brakes is 120 000 J in coming to a stop, how many meters did the car travel after the driver applied the brakes?
20m
Which of the following is an example of a wheel and axle?
A screwdriver
Increasing the length of a ramp ________ the efficiency of the ramp.
Decreases
The ratio of useful work output to work input is a measure of _________________
Efficiency
The ability to do work defines ____________________.
Energy
The law of conservation of energy states that
Energy can't be created nor destroyed
pair of tweezers is
compound machine made of two third-class levers.
Which of the following is not in the inclined plane family
A wheel and axle
A wheelbarrow is an example of a
2nd class lever
Power is calculated by dividing work by
Time
What is the mechanical advantage of a single fixed pulley?
1
medicine ball has a mass of 5 kg and is thrown with a speed of 2 m/s. What is its kinetic energy?
10 j
A weightlifter presses a 400 N weight 0.5 m over weightlifter?
100 watts
The efficiency of a ramp is 75%. If the amount of work input is 240 J, what is the amount of useful work output
180
What is the mechanical advantage of a single movable pulley?
2
object weighing 75 N is dropped from the top of a building and falls a distance of 28 m to the ground. How much work does gravity do on the object from the time it is dropped to the time it hits the ground?
2100 j
A man pushes a crate along a factory floor by exerting a force of 55 N. If the crate moves a distance of 4.0 m, how much work does the man perform?
220 n
What is the gravitational potential energy of a 55 kg box that is 8.0 m above the ground?
4300 j
What is the mechanical advantage of a ramp that is 10 meters long and 2 meters high?
5
Three children exhaust themselves trying to push a large rock that doesn't budge. Have they done any work? Why?
64. ANS: Work is defined as force times Work is done only when force causes a change in motion. distance. If the rock has not moved any distance, no work has been done.
An object has a kinetic energy of 810 J after falling a certain distance. If the mass of the object is 20 kg, what is the speed of the object at this time?
9 m/s
Do machines reduce the amount of work we have to do? If not, why are machines so useful?
A machine does not reduce the amount of work because the work input is always equal to or greater than the work output. Machines enable us to exert smaller forces over greater distances, greater forces over smaller distances, and/or change the direction of force.
Which of the following is a compound machine?
A pair of pliers
How does a pendulum show that there are nonmechanical forms of energy?
A pendulum with no external sources of energy will gradually stop swinging because of air resistance, friction, and other forces. Kinetic energy and gravitational potential energy are lost in the system. But because energy is never truly lost, the mechanical energy of the pendulum must be transformed into nonmechanical energy.
Which of the following processes requires the most work?
A person lifts a 1kg weight 1m off the floor
Gravitational potential energy depends on the
All of the above
What are the units of power?
All of the above
What are the units of work?
All of the above
Where does energy go when it seems to disappear?
Because energy can never truly disappear, when it seems to disappear, it is actually being converted into other forms of energy that cannot be observed directly. These may include chemical energy, nuclear energy, potential energy, or even kinetic energy.
A pendulum is swinging back and forth and has a kinetic energy of 400 J at a particular point in its path. Which of the following statements is not true?
Both the kinetic and potential energy are decreasing
A machine is a device that
Can multiply and change the direction of an input force
An inclined plane
Changes both the magnitude and the direction of the firce
The kind of energy associated with atomic bonds is
Chemical
The source of the energy when dynamite explodes is ____________________ energy.
Chemical
____________________ is defined as a machine made up of more than one simple machine
Compound machine
If a person tries to lift a heavy box for 5 seconds and cant make it budge, the work done on the box is __________ zero
Equal to
Machines decrease the amount of energy that is needed to do work.
False
All levers have a rigid arm that turns around a point called the
Fulcrum
Which of the following is an example of a third-class lever?
Hand held boat paddle
Which of the following statements is not true?
If the kinetic energy of an object decreases, the nonmechanical energy will decrease.
The formula for calculating kinetic energy can be written as ____________________.
KE=1/2mv2
The energy of a moving object due to its motion is called ____________________.
Kinetic energy
Why is light considered a form of energy?
Light is considered a form of energy because it transforms into other kinds of energy, and other kinds of energy are the source of light. Photosynthesis, for example, converts light energy into chemical energy. In the sun, nuclear energy is converted into light energy. Light is also considered a form of energy because it can do work.
quantity that measures how much a machine multiplies force or distance is called ____________________.
Mechanical advantage
The sum of the kinetic and potential energy of large-scale objects in a system is called ____________________.
Mechanical energy
Energy that lies at the level of atoms and does not affect motion on a large scale is sometimes called ____________________ energy.
Non mechanical
What is nuclear fission?
Nuclear fission is the nuclear reaction that provides the energy for nuclear power plants. Nuclear energy is released when a single heavy nucleus is split into two or more lighter nuclei.
59. The source of the sun's energy is ____________________.
Nuclear fusion
The primary source of the sun's energy is
Nuclear fusion
What is nuclear fusion?
Nuclear fusion is the nuclear reaction that gives the sun its energy. The nuclear energy is released when light atomic nuclei combine to form a heavier nucleus.
Increasing the angle a ramp makes with the horizontal decreases the mechanical advantage.
True
A ball falling under the force of gravity is a ________system.
Open
A meteorologist trying to predict global warming would consider Earth to be a _______ system
Open
. A(n) ____________________ exchanges energy with the outside
Open system
60. When a system exchanges energy with the environment outside the system, it is called a(n) ____________________
Open systen
process that transforms light energy into chemical energy in plants is called __________
Photosythesis
Which of the following is an example of mechanical energy?
Potential
The stored energy resulting from the relative positions of objects in a system is called ____________________.
Potential energy
A quantity that measures the rate at which work is done is called ____________
Power
An arrangement of multiple pulleys causes the direction of the output force to be ________ to the direction of the input force.
Same as
What is the difference between an open system and a closed system?
Scientists must carefully define the area or objects they are studying; that is, they must define the system under consideration. If the energy flowing into or out of the system is significant, then the system is open. If the energy flowing into or out of the system is insignificant, the system is said to be closed.
Which of the following is not a simple machine?
Scissors
A(n) ____________________ is an inclined plane wrapped around a cylinder.
Screw
What is the law of conservation of energy?
The law of conservation of energy states that energy cannot be created or destroyed. This means that when energy transforms from one kind of energy to another, the total amount of energy before the transformation is exactly equal to the amount of energy after the transformation.
What is meant by the efficiency of a machine?
The work output of a machine is generally less than the work input, because additional force is needed to overcome the effects of friction and other forces. You can measure efficiency by dividing the work output by the work input.
A first-class lever can have an input force greater force than the output force.
True
A second-class lever always has an input force that is less than the output force.
True
Because of friction, using machines increases the amount of energy that is needed to do work
True
Horsepower is the common unit of power in rating engines. However, the official SI unit of power is the
Watt
How does a pendulum show the relationship between gravitational potential energy and kinetic energy?
When a pendulum swings back and forth, it goes from having zero kinetic energy at the top of its path to having a maximum amount of kinetic energy at the bottom of its path. At the same time, it goes from having a maximum amount of gravitational potential energy to having a minimum amount of gravitational potential energy. Energy is changing form back and forth between kinetic energy and gravitational potential energy.
Why does a fixed pulley have a mechanical advantage of 1 and a movable pulley have a mechanical advantage of 2?
When a pulley is stationary, the input distance is equal to the output distance, so the input force must be equal to the output force. When the pulley moves, the input distance is twice as great as the output distance, so the input force is half the output force.
Which of the following statements about work and energy is not true?
Work and energy are always equal
A boy pushes on a parked car with a force of 200 N. The car does not move. How much work does the boy do on the car?
Zero
A first-class lever has the
fulcrum in the middle.