Question 1| 1.61 points | Save |
| You are standing on a scale in an elevator. Suddenly you notice your weight decreases. What do you conclude?| | | | | | | | The elevator is accelerating downwards.|
| | The elevator is moving at a constant velocity downwards.| | | The elevator is moving at a constant velocity upwards.| | | Your diet is working.|
| | The elevator is accelerating upwards.|
| | | | |

Question 2| 1.61 points | Save |
| Tidal friction caused by the earth's stretching from the Moon's gravity is gradually slowing down the rotation of the earth.| | | | | | | True|
| False|
| | | | |

Question 3| 1.61 points | Save |
| If your mass is 60 kg on Earth, what would your mass be on the Moon?| | | | | | | | 10 kg|
| | 60 lb|
| | 50 kg|
| | 10 lb|
| | 60 kg|
| | | | |

Question 4| 1.61 points | Save |
| In which of the following cases would you feel weightless?| | | | | | | | while walking on the Moon|
| | while falling from an airplane with your parachute open| | | while falling from a roof|
| | while traveling through space in an accelerating rocket| | | none of the above|
| | | | |

Question 5| 1.61 points | Save |
| Which of the following best describes the origin of ocean tides on Earth?| | | | | | | | The Moon's gravity pulls harder on water than on land, because water is less dense than rock.| | | Tides are caused by the 23 1/2° tilt of the earth's rotational axis to the ecliptic plane.| | | Tides are caused primarily by the gravitational force of the Sun.| | | Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the earth.| | | Tides are caused on the side of the earth nearest the Moon because the Moon's gravity attracts the water.|

...WORK and ENERGY
Work done by a constant force
1- The drawing shows a plane diving toward the ground and then climbing back upward. During each of these motions, the lift force acts perpendicular to the displacement , which has the same magnitude, 1.7 × 103 m, in each case. The engines of the plane exert a thrust , which points in the direction of the displacement and has the same magnitude during the dive and the climb. The weight of the plane has a magnitude of 5.9 × 104 N. In both motions, net work is performed due to the combined action of the forces , and .
a. Is more net work done during the dive or the climb? Explain.
b. Find the difference between the net work done during the dive and the climb.
Answer:
a. More net work is done during the dive.
b. 6.8 × 107 J
2- Find the work done by a force through a displacement of 3m in the positive x direction
Work-Energy theorem and kinetic energy
3- The mass of the space probe is 474-kg and its initial velocity is 275 m/s. If the 56.0-mN force acts on the probe through a displacement of 2.42×109m, what is its final speed?
Answer:
4- Example 2: Skier
Gravitational PotentialEnergy, Conservative versus Nonconservative Forces
5- The gymnast leaves the trampoline at an initial height of 1.20 m and reaches a maximum height of 4.80 m before falling back down. What was the initial speed of the...

...PotentialEnergy
• Definition and Mathematics of Work
• Calculating the Amount of Work Done by Forces
• PotentialEnergy
• Kinetic Energy
• Mechanical Energy
• Power
An object can store energy as the result of its position. For example, the heavy ball of a demolition machine is storing energy when it is held at an elevated position. This stored energy of position is referred to as potentialenergy. Similarly, a drawn bow is able to store energy as the result of its position. When assuming its usual position (i.e., when not drawn), there is no energy stored in the bow. Yet when its position is altered from its usual equilibrium position, the bow is able to store energy by virtue of its position. This stored energy of position is referred to as potentialenergy. Potentialenergy is the stored energy of position possessed by an object.
Gravitational PotentialEnergy
The two examples above illustrate the two forms of potentialenergy to be discussed in this course - gravitational potentialenergy and elastic potentialenergy. Gravitational potential...

...the transfer of energy; work is done on an object when an applied force moves it through a distance. The link between work and energy is work done equals energy transferred. The units for the two are also the same (joules). E.g. 500J of work = 500J of kinetic energy.
Work is calculated with the formula: work done=force x distance moved
For example, if a force of 10 newton (F = 10 N) acts along point that travels 2 meters (d = 2 m), then it does the work W = (10 N)(2 m) = 20 N m = 20 J. This is approximately the work done lifting a 1 kg weight from ground to over a person's head against the force of gravity. Notice that the work is doubled either by lifting twice the weight the same distance or by lifting the same weight twice the distance.
Examples:
Force is measured in newton’s (N)
Distance is measured in meters (M)
Work done is measured in joules (J)
Examples of work done:
How much work is done by a person who uses a force of 27.5N to move a grocery buggy 12.3m?
W = F x d = (27.5N) (12.3m) = ?
Equation
W = 338.25J
Answer
55, 000J of work is done to move a rock 25m. How much force was applied?
F = W = 55,000J = ?
d 25m
Equation
F = 2200J
Answer
You and 3 friends apply a combined force of 489.5N to push a piano. The amount of work done is 1762.2J. What distance did the piano move?
Equation
d= W = 1762.2J =
F 489.5N
Answer
d = 3.6m...

...Assignment: (Physics)
1. What is energy?
2. Differentiate Potential from Kinetic Energy
3. Differentiate Gravitational PotentialEnergy from Elastic PotentialEnergy
1. In physics, energy is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical systems. However, this must be understood as an overly simplified definition, as the laws of thermodynamics demonstrate that not all energy can perform work.
2. Kinetic energy is the energy something has because it is moving. Potentialenergy is the energy something has because of its position or configuration.
3. Gravitational energy is the potentialenergy associated with gravitational force. If an object falls from one point to another point inside a gravitational field, the force of gravity will do positive work on the object, and the gravitational potentialenergy will decrease by the same amount.
When accounting only for mass, gravity, and altitude, the equation is:
U = mgh
where U is the potentialenergy of the object relative to its being on the Earth's surface, m is the mass of the object, g is the acceleration due to gravity, and h is the...

... Efficiency (%) = Useful Energy Out x 100
Total Energy In
Questions
1) A light bulb takes in 30J of energy per second. It transfers 3J as useful light energy and 27J as heat energy. Calculate the efficiency.
2) A kettle takes in 2000J of energy per second. It transfers 1500J as useful heat energy and 500J is wasted as soundenergy. Calculate the efficiency of the kettle.
Remember: In the exam they may not ask for efficiency as a percentage!!!
3) Calculate the efficiency of a hair dryer which takes in 3000J of energy per second and transfers 600J as useful heat energy. Express your answer as a decimal and not as a percentage.
4) Calculate the efficiency of a TV which takes in 5000J of energy per second and transfers 1000J as useful light energy and 1500J as useful sound energy. The remaining 2500J is wasted as heat energy. Express your answer as a decimal and not a percentage.
Extended Questions (Includes Work, Energy & Power)
1. Calculate the efficiency of a light bulb that gives of 40J of light from 200J of electrical energy.
2. Calculate the percentage efficiency of a motor that does of 60J of work from 240J of electrical energy.
3....

...Holt Physics—Chapter 5: Work and Energy Price
I. Section 5.1—Work
A. Definition of work
1. Work does not mean the same thing in Physics as it does in the everyday sense of the word.
2. Work is defined as a force causing a displacement.
Work = force x displacement
W = Fd
3. Work is NOT done on an object unless the displacement is greater than zero
4. The only forces that are considered to do work are those that are parallel to the displacement.
5. For this reason we use our trigonometric functions to calculate forces applied at an angle.
Insert Fig 5-2
6. Note that Θ is the angle between the applied force and the displacement.
7. Work is described in Newtons x meters (force x displacement). The unit of work is the Joule (J)
8. 1 Newton meter = 1 Joule
9. Work is a vector with both direction AND magnitude. This means WORK CAN BE NEGATIVE!
10. Negative work is most commonly used to slow an object down or decrease its velocity.
II. Section 5-2: Energy
A. Kinetic Energy
1. Kinetic energy is associated with an object in motion.
2. Kinetic energy depends on speed and mass
Kinetic...

...Kinetic Energy:
Consider a baseball flying through the air. The ball is said to have "kinetic energy" by virtue of the fact that its in motion relative to the ground. You can see that it is has energy because it can do "work" on an object on the ground if it collides with it (either by pushing on it and/or damaging it during the collision).
The formula for Kinetic energy, and for some of the other forms of energy described in this section will, is given in a later section of this primer.
PotentialEnergy:
Consider a book sitting on a table. The book is said to have "potentialenergy" because if it is nudged off, gravity will accelerate the book, giving the book kinetic energy. Because the Earth's gravity is necessary to create this kinetic energy, and because this gravity depends on the Earth being present, we say that the "Earth-book system" is what really possesses this potentialenergy, and that this energy is converted into kinetic energy as the book falls.
Thermal, or heat energy:
Consider a hot cup of coffee. The coffee is said to possess "thermal energy", or "heat energy" which is really the collective, microscopic, kinetic and potentialenergy of the molecules in the coffee...

...Tutorial – Work, Energy
(Assume the acceleration due to gravity, g = 9.81 m/s2 )
1. Calculate the work done when a force of 40 N pushes an object a distance of
500 m in the same direction as the force.
2. Calculate the work done when a mass is lifted vertically by a crane to a height of 5 m, the force required to lift the mass being 98 N.
3. A spring, initially in a relaxed state, is extended by 100 mm. Determine the work done by using a work diagram if the spring requires a force of 0.6 N per mm of stretch.
4. A spring requires a force of 10 N to cause an extension of 50 mm. Determine the work done in extending the spring (a) from zero to 30 mm, and (b) from 30 mm to 50 mm.
5. Calculate the work done when a mass of 20 kg is lifted vertically through a distance of 5.0 m. Assume that the acceleration due to gravity is 9.81 m/s2 .
6. Water is pumped vertically upwards through a distance of 50.0 m and the work done is 294.3 kJ. Determine the number of litres of water pumped. (1 litre of water has a mass of 1kg).
7. Determine the work done when a force of 50 N pushes an object 1.5 km in the same direction as the force.
8. Calculate the work done when a mass of weight 200 N is lifted vertically by a crane to a height of 100m.
9. A spring requires a force of 50 N to cause an extension of 100 mm. Determine the work done in extending the spring (a) from 0 to 100 mm, and (b) from 40 mm to 100 mm.
10. A machine exerts a...