1. Explain how you could move an object and still do no work. 2. Explain the dif
ID: 1429167 • Letter: 1
Question
1. Explain how you could move an object and still do no work.
2. Explain the difference between the everyday use of the word “work” and the physical (physics related) use of the word “work”. How is energy related to work?
3. An initially stationary 15.0-kg crate of cheese wheels is pulled via a cable a distance d= 5.70m up a frictionless ramp to a height of h= 2.50m, where it stops. What is the potential energy of the crate after it is lifted? How much work is done during the lift? If it takes 10 seconds to lift the cheese, what is the power rating of the lifting device?
4. In a simulation on earth, an astronaut in his space suit climbs up a vertical ladder. On the moon, the same astronaut makes the same climb. In which case does the gravitational potential energy of the astronaut change by a greater amount? Account for your answer.
5. A 2000 kg car is moving with a velocity of 50 km/hr. What is its kinetic energy? If the car reduces its speed by half, by what factor is the kinetic energy changed?
6. State the Law of Conservation of Energy. Give an example of a system where energy is conserved.
Explanation / Answer
1. "we could move an object and still do no work" with explanations which given as :
we know that, W = F d
For example; Pick up a book from the table. Take it to school and then, after school bring it home and place it exactly where we picked it up from.
it means that, "No work has been done, as the book is where it originally was, it has not moved any distance".
2. Work and energy are important concepts in physica as well as in our daily everyday life.
In physics, a force does work when it acts on an object that moves through a distance and there is a component of the force along the line of motion. For a constant force in one dimension, the work done equals the force time the distance.
In everyday use, when we study hard for an exam, the only work we do as the term is understood in physics is in moving our pencil or turning the pages of our book.
Energy is related to work. When work is done by one system on another system, energy is transferred b/w the two systems.
3. The potential energy of the crate after it lifted which will be given as :
using a formula, we have
P.E = m g h = (15 kg) (9.8 m/s2) (2.5 m)
P.E = 367.5 J
During the lift, work done is given as :
we know that, K.E = P.E = W
W = 367.5 J
If it takes 10 seconds to lift the cheese, then the power rating of the lifting device will be given as :
P = W / t = (367.5 J) / (10 s)
P = 36.7 W
5. Its kinetic energy is given by, K.E = (1/2) m v2
where, v = speed = 50 km/hr = 13.89 m/s
K.E = (0.5) (2000 kg) (13.89 m/s)2
K.E = 192932.1 J
6. The "Law of Conservation of Energy" states that the total amount of energy remains constant in an isolated system. It implies that energy can neither be created nor destroyed, but can be change from one form to another.
For example ; When a moving car hits a parked car and causes the parked car to move, energy is transferred from the moving car to the parked car.
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