Physics Chapter 5 Test
Which equation is used to calculate the work done on an object by a force at an angle, θ, to the displacement?
W = (F)(d)(cosθ)
When, and only when, is work done?
When components of a force are parallel to a displacement
A construction worker lifts a heavy cinder block 1 m off the ground, holds it in place for 3 s, then sets it back down in the same place. Describe the forces doing work on the block and the net work on the block throughout this action.
When the worker first lifts the block it is positive work, but at the same time gravity is negative. However, because the block is still lifted there is an overall positive net work. Also when he lowers the block, the worker still applies a smaller positive force to lower it without dropping it. Gravity is also still a negative force when he lowers it.
A painter lifts a bucket of paint, carries it 5 m horizontally, then sets it back down. Which of the following is true? a. The force of gravity does negative work when the worker lifts the bucket. b. The painter does positive work on the bucket when carrying it horizontally at constant speed. c. The painter does positive work on the bucket when setting it down. d. No net work is done on the bucket.
A.
Energy associated with a compressed or stretched object is...?
Elastic Potential Energy
In which of the following cases is no work done? a. A weightlifter lifts a barbell. b. A weightlifter holds a barbell overhead. c. A weightlifter slowly lowers a barbell. d. A weightlifter drops a barbell and the barbell falls to the ground.
B.
A parachutist falls at a constant speed for 200 m. Which of the following is true? a. The force of gravity is the only force doing work on the parachutist. b. Air resistance is the only force doing work on the parachutist. c. No forces are doing work on the parachutist. d. No net work is done on the parachutist.
D.
Which of the following does not affect gravitational potential energy? a. an object's mass b. an object's height relative to a zero level c. the free-fall acceleration d. an object's speed
D.
Which of the following sentences uses work in the scientific sense. a. Stan goes to work on the bus. b. Anne did work on the project for 5 hours. c. Joseph found that holding the banner in place was hard work. d. An engine does work on a car when the car is moving.
D.
Energy stored in the gravitational field of interacting bodies is...?
Gravitational Potential Energy
What is the equation of kinetic energy?
KE = (1/2)mv² [Kinetic Energy = (1/2) (mass) (speed)²
Energy that is due to the motion of an object is...?
Kinetic Energy
What are the mechanical energies?
Kinetic and Potential
A joule is equivalent to...?
N × M
What are the units for the spring constant?
N/M (Newton/Meter)
What is the equation Elastic Potential Energy?
PEe = (1/2)kx² [Elastic Potential Energy = (1/2) Spring Constant × Distance compressed or stretched
What is the equation for Gravitational Potential Energy?
PEg = mgh (Gravitational Potential Energy = mass × free fall acceleration × height)
What are the non mechanical energies?
Solar, Thermal, Electrical, Magnetic, and Nuclear
Which has more kinetic energy, a 4.0 kg bowling ball moving at 1.0 m/s or a 1.0 kg bocce ball moving at 4.0 m/s? Explain your answer.
The bocce ball because it is going faster. The speed is squared, mass is not.
If the sign of work is negative, then...?
The component of the force that does work is in the direction opposite the displacement.
How does the elastic potential energy in a mass-spring system change if the displacement of the mass is doubled?
The elastic potential energy does not change.
Friction does -400 J of net work on a moving car. How does this affect the kinetic energy of the car?
The kinetic energy decreases by 400 J.
How does the kinetic energy of an object change if the object's speed doubles?
The kinetic energy increases by a factor of 4.
If a neighbor pushes a lawnmower four times as far as you do but exerts only half the force, which one of you does more work and by how much?
The neighbor; 2x more
Work-Kinetic Energy Theorem
The net work done by all the forces acting on an object is equal to the change in the object's kinetic energy
The work-kinetic energy theorem states that...?
The net work done on an object equals the change in the kinetic energy of the object.
What the equation for the Work-Kinetic Energy Theorem?
Wnet = (1/2)m (vf² - vi²) [Net Work = (1/2) mass × (final velocity² - initial velocity²)]
Work is done on an object whenever...?
a force causes a displacement of the object.
For each of the following cases, indicate whether the work done on the second object in each example will have a positive or a negative value. a. The road exerts a friction force on a speeding car skidding to a stop. b. A rope exerts a force on a bucket as the bucket is raised up a well. c. Air exerts a force on a parachute as the parachutist falls to Earth.
a. Negative b. Positive c. Negative
Determine whether work is being done in each of the following examples. a. a train engine pulling a loaded boxcar initially at rest b. a tug of war that is evenly matched c. a crane lifting a car
a. Yes b. No c. Yes
What is Potential Energy?
the energy associated with an object because of the position, shape, or condition of the object
What is Elastic Potential Energy?
the energy available for use when a deformed elastic object returns to its original configuration
Kinetic Energy
the energy of an object that's due to the object's motion
What is Gravitational Potential Energy?
the potential energy stored in the gravitational fields of interacting bodies