MOPS Work and Energy
If an object has kinetic energy, then it will not have any potential energy.
False
If an object is moving along the ground, then it will not have any kinetic energy.
False
In order to have work done upon an object, there must be a(n) ___ to cause a(n) ___.
force acting upon the object, displacement
Consider the types of forces present in the following physical situation: A parachutist is falling downward, encountering a large amount of air resistance. In this situation, the total mechanical energy of the parachutist ___.
will definitely change
Consider the types of forces present in the following physical situation: A dart is traveling through the air towards a dart board. Assume that air resistance is negligible. In this situation, the total mechanical energy of the dart ___.
will remain constant
Consider the types of forces present in the following physical situation: A roller coaster car is coasting down the first drop of the track. Assume that resistance forces have no effect on the car's motion. In this situation, the total mechanical energy of the car ___.
will remain constant
A man is walking through an airport with a suitcase. The man exerts a constant upward force upon the suitcase as he walks a distance of 20 meters. In this example the man is doing ___ work upon the suitcase.
zero (suitcase is not being displaced relative to the man)
The standard metric unit of power is a ___.
Watt
Power is defined as ___ .
the rate at which work is done upon an object
The total mechanical energy of an object is ___.
the sum of its kinetic energy and potential energy
An object starts at rest from a height of 30 meters. It's total amount of mechanical energy is 300 Joules. The object begins a free-falling motion; there is no air-resistance. When it has fallen to a height of one-third of its original height, its potential energy will be ___ Joules and its total amount of mechanical energy will be ___ Joules. Enter the two answers in order; no commas; no spaces.
100, 300
A horizontal force of 80 Newton is applied to a 10-kg crate to move it horizontally a distance of 4 meters across a concrete floor at a constant speed of 2 m/s. The task requires 2 seconds. The power rating for the person applying the force is approximately ___ W.
160 (W=Fd, P=W/t)
A 55-kg mountain climber ascends (climbs) 15 meters up a steep cliff in 45 seconds. The power rating of the mountain climber is approximately ___ W.
183 (W=Fd, P=W/t)
An object has a kinetic energy of 18 J. If the object's speed is decreased to one-third of its original value, then its new kinetic energy will be ___ J.
2 (times 1/3 twice)
Jack and Jill are doing a physics lab. They apply a 15-Newton force to a 3-kg cart to pull it up an inclined plane at a constant speed. The plane in inclined at a 30-degree angle. Jack and Jill are exerting a force on the cart that is parallel to the inclined plane in order to displace it 2.0 meters along the incline to a final height of 1 meter. During this lab, the amount of work done on the cart is approximately ___ Joules.
30 Joules (Since the force applied is parallel to the inclined plane, you do not need to use law of cosines, you just use the equation W=Fd)
A 8-kg object is moving with a speed of 5 m/s at a height of 4 m. The potential energy of the object is approximately ___ J.
320 (mgh)
A 5-kg object is moving with a speed of 4 m/s at a height of 2 m. The kinetic energy of the object is approximately ___ J.
40 (.5mv^2)
A roller coaster car is nearing the end of the track and approaching the loading dock. It possesses 300000 Joules of kinetic energy and 50000 Joules of potential energy. A resistive force of 10000 Newtons is applied to the car over a distance of 25 meters along a level section of the track. The new kinetic energy of the roller coaster car is ___ Joules.
50000 (300000-(25x10000))
A boy in a wagon is moving along a level sidewalk. Together, the boy and the wagon have 30 joules of kinetic energy. The boy's older brother applies a 20-Newton horizontal force for a distance of 2 meters. The kinetic energy of the boy and the wagon is now ___ Joules.
70 (30+(20x2))
In a physics lab, a 60-kg student runs up a 2.0-meter tall flight of stairs in 1.5 seconds. The student's power rating is approximately ___ W.
800 (W=Fd, P=W/t)
Consider the three situations described below. In which situation(s) would the mechanical energy NOT be conserved? Include all that apply; no commas; no spaces.
A car skids to a stop across a level highway A mountain climber slow but steadily ascends a steep cliff
Which of the following are examples of work being done (either positive or negative) upon the object? Include all that apply; no commas; no spaces.
A rightward force is applied to an object to move it to the right at a constant speed A rightward force is applied to an object to accelerate it to the right An upward force is applied to an object to accelerate it upward An upward force is applied to an object to move it upward at a constant speed An upward force is applied to a downward moving object to slow it down as it moves (All of these cause displacement)
A 5-Newton force is applied to a 2-kg object to move it across a horizontal surface at a constant speed for a distance of 4 meters. The free-body diagram is shown. Which of the following forces are doing work upon the object - either positive or negative?
Applied force Friction force
A feather is slowly falling at a constant terminal velocity from an 80-foot elevation (initial state) to just above the ground level (final state).
Change to Negative Work Cross out PEi
A skydiver is falling at a constant terminal velocity from a 1000-foot elevation (initial state) to just above ground level (final state).
Change to Negative Work Cross out PEi
A sledder begins from rest at the top of a small hill (initial state) and slides to ground level at the bottom of the hill (final state). Friction and air resistance influence the motion.
Cross out KEi Change to Negative Work Cross out PEf
A car accelerates from rest (initial state) along a level roadway to a high speed (final state).
Cross out KEi Cross out PEi Cross out PEf
A sprinter accelerates from rest (initial state) along a level track to a high speed (final state).
Cross out KEi Cross out PEi Cross out PEf
A spring-loaded dart gun mounted at ground level (initial state) launches a dart upward at a 45-degree angle. The dart ascends upwards to the peak of its trajectory (final state). Neglect air resistance.
Cross out KEi Cross out Work
A sledder begins from rest on the top of a hill (initial state) and slides effortlessly to ground level at the bottom of the hill (final state). Assume negligible friction and air resistance.
Cross out KEi Cross out Work Cross out PEf
A roller coaster car begins from rest at a location on top of the first drop (initial state) and coasts to the ground level at the bottom of the drop (final state). Assume negligible friction and air resistance.
Cross out KEi Cross out Work Cross out PEi
Some forces are categorized as conservative forces (or internal forces) while others are categorized as non-conservative forces (or external forces). Which of the following forces are generally categorized as non-conservative (or external) forces? Include all that apply; no commas; no spaces.
Force of Friction Applied Force Normal Force Air Resistance Force Tension Force
Some forces are categorized as conservative forces (or internal forces) while others are categorized as non-conservative forces (or external forces). Which of the following forces are generally categorized as conservative (or internal) forces?
Force of Gravity Spring Force
Some forces are categorized as conservative forces (or internal forces) while others are categorized as non-conservative forces (or external forces). Which of the following forces are generally categorized as conservative (or internal) forces? Include all that apply; no commas; no spaces.
Force of Gravity Spring Force
A 5-Newton friction force acts upon a 2-kg object to slow it down as it moves it across a horizontal surface over a distance of 4 meters. The free-body diagram is shown. Which of the following forces are doing work upon the object - either positive or negative? Include all that apply; no commas; no spaces.
Friction force
Which of the following variations will increase the potential energy of an object? Include all that apply; no commas; no spaces.
Increase the object's height Increase the object's mass
Which of the following variations will increase the kinetic energy of an object? Include all that apply; no commas; no spaces.
Increase the object's mass Increase the object's speed
The standard metric unit of work is the
Joule
If the only forces doing work upon an object are conservative (or internal) forces, then the total mechanical energy of the object will ___. If the only forces doing work upon an object are non-conservative (or external) forces, then the total mechanical energy of the object will ___. Enter the two letters in order; no commas; no spaces.
Not change, change - either increase or decrease
Consider the diagram. The kinetic energy and the potential energy of a roller coaster car at various locations are shown. The total mechanical energy of the car at position D is ___ Joules.
PE+KE=ME
If non-conservative forces (i.e., external forces) are acting upon an object, then the total mechanical energy of that object could still remain constant.
True
Consider the motion of the roller coaster car shown in the diagram below. The kinetic energy (KE) and the potential energy (PE) values are shown for various locations. In this example, ___. Include all that apply; no commas; no spaces.
total mechanical energy is conserved
Consider the types of forces present in the following physical situation: A bucket full of water is slowly lifted by a rope out of a deep well. In this situation, the total mechanical energy of the bucket of water ___.
will definitely change
Consider the types of forces present in the following physical situation: A car is skidding to a stop. In this situation, the total mechanical energy of the car ___.
will definitely change
If both conservative forces (i.e., internal forces) are doing net work upon an object, then the total mechanical energy of the object ___.
will definitely change
A 18-Newton force is applied parallel to an inclined plane in order to move a 2.8-kg cart from ground level a distance of 1.2 meters along the inclined plane to the top at a constant speed. The potential energy of the cart at the top of the incline is approximately ___ Joules.
21.6 (W=Fd)
If an object has potential energy, then it will not have any kinetic energy.
False
If an object is moving, then it will not have any potential energy.
False
The essential difference between work and power is that power is ___.
a rate quantity and work is not a rate quantity
If the total mechanical energy of an object is conserved, then ___.
the sum of the KE and the PE is the same for the initial state as it is for the final state
When an object's total mechanical energy is NOT conserved, ___. Include all that apply; no commas; no spaces.
the sum of the kinetic energy and the potential energy is changing mechanical energy is being converted into non-mechanical forms (or vice versa)
Student A and student B are doing two identical tasks involving physical work. Student A does the task in more time than student B. In this physical situation, ___.
the two students do the same amount of work but student B has the greater power rating
Two objects of identical mass begin from rest at the same height at the top of two different hills - hill A and hill B. The hills are inclined at two different angles (see diagram). The objects are released from rest and slide to the bottom; resistance forces can be considered to be negligible. The object of top of hill ___ will have the smallest speed at the bottom of the incline.
... nonsense! Both objects will have identical speeds at the bottom
A 1400-kg car moving with a speed of 32 m/s is approaching a stoplight. The light turns yellow and the car makes an abrupt stop over a distance of 60 meters. The amount of mechanical energy that is converted to heat and other non-mechanical forms is approximately ___ Joules.
716800 (.5mv^2)
Consider the work energy bar charts shown below. Tap on the letter of any bar chart that portrays a situation in which mechanical energy is NOT conserved.
Any chart where work is being done
A skier pulled by a tow rope from the bottom of a training hill (initial state) to the top of the training hill (final state) at a constant speed.
Cross out PEi
A small physics cart is pulled from the bottom of a ramp (initial state) to the top of the ramp (final state) at a constant speed.
Cross out PEi
A car moving with a high speed at the bottom of a hill (initial state) runs out of gas and coasts to a stop as it moves up towards the top of the hill (final state). Friction and air resistance influence the motion.
Cross out PEi Change to Negative Work Cross out KEf
A baseball player moving with a speed of 8.5 m/s (initial state) dives head-first and slides to a stop (final state) along level ground.
Cross out PEi Change to Negative Work Cross out KEi Cross out PEi
A sledder is moving with a high speed at the bottom of a hill (initial state) and gradually coasts to a stop as it moves to the top of the hill (final state). Ignore all frictional forces.
Cross out PEi Cross out Work Cross out KEi
A roller coaster car coasts from position A to position B (as shown in the diagram below). Resistance forces are negligible. At position B, the total mechanical energy of the car is ___ Joules and the kinetic energy is ___ Joules. Enter the two answers in order; no commas; no spaces.
KE+PE=ME, ME-PE=KE
Mac and Tosh run up the same hill. Mac has twice the mass as Tosh. Tosh climbs up the hill in one-half the time as Mac. In this situation, ___.
Mac does more work than Tosh, but they have the same power rating
Suppose an object moves downward with a decreasing speed. In this situation, the object's kinetic energy would ___, its potential energy would ___, and its total mechanical energy would ___. Enter the three letters in order; no commas; no spaces.
decrease, decrease, decrease
Suppose an object slows down while moving horizontally. In this situation, the object's kinetic energy would ___, its potential energy would ___, and its total mechanical energy would ___. Enter the three letters in order; no commas; no spaces.
decrease, remain the same, decrease
Suppose an object moves upward with an increasing speed. In this situation, the object's kinetic energy would ___, its potential energy would ___, and its total mechanical energy would ___. Enter the three letters in order; no commas; no spaces.
increase, increase, increase
Suppose an object speeds up while moving horizontally. In this situation, the object's kinetic energy would ___, its potential energy would ___, and its total mechanical energy would ___. Enter the three letters in order; no commas; no spaces.
increase, remain the same, increase
Kinetic energy is the energy that an object possesses due to its ___ and potential energy that an object possesses due to its ___.
motion, position
An object will have kinetic energy if it is ___. Include all that apply; no commas; no spaces.
moving moving on the ground (height = 0 m) moving above the ground (a non-zero height)
An object will definitely have potential energy if it is ___.
moving above the ground (a non-zero height) at rest above the ground (a non-zero height)
A softball player is sliding into third base. Once she hits the dirt, the force of friction acts upon her to slow her down as she slides a distance of 1.5 meters across the dirt. In this example, friction is doing ___ work upon the player.
negative (friction is SLOWING her down)
In order for an object to conserve its total mechanical energy it is absolutely necessary that ___.
non-conservative (i.e., external) forces do NOT do net work upon the object
An object's mechanical energy will NOT be conserved if ___.
non-conservative forces (i.e., external forces) are doing work upon the object
If the only forces doing work upon an object are conservative (or internal) forces, then the total mechanical energy of the object will ___. If the only forces doing work upon an object are non-conservative (or external) forces, then the total mechanical energy of the object will ___. Enter the two letters in order; no commas; no spaces.
not change, change - either increase or decrease
A child is pushing an empty box across a living room floor. The child exerts a constant rightward force upon the box to move it a distance of 2 meters to the right. In this example, the child is doing ___ work upon the box.
positive (rightward force causes displacement in a positive direction)
Suppose an object moves downward at a constant speed. In this situation, the object's kinetic energy would ___, its potential energy would ___, and its total mechanical energy would ___. Enter the three letters in order; no commas; no spaces.
remain the same, decrease, decrease
Suppose an object moves upward at a constant speed. In this situation, the object's kinetic energy would ___, its potential energy would ___, and its total mechanical energy would ___. Enter the three letters in order; no commas; no spaces.
remain the same, increase, increase
Work is ___ quantity; it is fully described by stating its ___.
scalar, magnitude alone