anonymous 4 years ago PHYSICS QUESTION. helpppp with this last problem.

1. anonymous

An object's mass is 50 KG. 1- what is its potential energy relative to the ground if its height is 20 meters above the earth? 2- What is its potential energy relative to the ground if the objet is raised from 20m to 100 m? 3- what is the gain in potential energy? 4- What is the gain in total mechanical energy ? (assuming the object at rest at both 20 and 100 m)

2. anonymous

5- What is the amount of work applied to the object to raise it from 20m to 100m? 6- what is the amount of force applied to raise it? 7- what is the weight of the object? 8 - why is the weight equal the force acting on the object lift it? 9 - what is the power of the machine used to do lifting if the process took 5s to complete?

3. anonymous

What is the equation for potential energy?

4. anonymous

m * g * y

5. anonymous

Correct. So what is the potential energy when y = 20?

6. anonymous

So 1 = 9800 J and 2 = 39200J but with 3 i subract 39200 - 9800?

7. anonymous

Yes, yes, and yes!

8. JamesJ

@nikkysterr: don't forget eashmore some medals for his help!

9. anonymous

whooo ! alright but it confuses me when it comes to "object at rest"

10. anonymous

For #4, total mechanical energy is the sum of potential and kinetic energies. If an object is at rest, what is it's kinetic energy?

11. anonymous

0?

12. anonymous

Correct. So what is the total mechanical energy?

13. anonymous

Mechanical Energy is zero.

14. anonymous

I'm having some internet trouble. Forgive me if my responses are delayed.

15. anonymous

no problem i appreciate your help.

16. anonymous

physics isnt my strongest subject.

17. anonymous

Nope. Mechanical Energy (ME) is defined as such$ME = KE + PE$If KE is zero, we still need to account for PE.

18. anonymous

so mechanical energy isnt zero?

19. anonymous

Nope. It is equal to potential energy in this case.

20. anonymous

Oh so the mechanical energy would be the Potential Energy?

21. anonymous

for the amount of work how do i find the force?

22. anonymous

i know i have the distance 80 [100-20]

23. anonymous

but i need the force. to get the work.

24. anonymous

Nope. To find the work, we can use the work-energy theorem which is defined as$W = \Delta ME = \Delta KE + \Delta PE = \Delta PE$

25. anonymous

We will find the force from this value of work, using the definition of work you are thinking of. You're on the right track.

26. anonymous

the work force is equal to the PE.

27. anonymous

Work is equal to the same answer we got for number 3.

28. anonymous

because i was thinking w = f times d. and force = mass times acceleration i

29. anonymous

Now, from this value$W = F \cdot y$We can find the force from this expression, using the value from work obtained in number 5.

30. anonymous

so it would be 9800J = f * 80?

31. anonymous

Yes. I must leave now. I'll leave you with an outline of what to do: I must leave. I'll outline the solution to the remainder of the questions: 5. The amount of work comes from the definition of work I gave you earlier. $W = \Delta U = \Delta KE + \Delta PE = \Delta PE$ 6. Comes from the other definition of work. $W = F \cdot y$We know the work from part 5, and the distance we move in y (100 - 20). We can solve for y. 7. Weight is equal to (mass)x(gravity) 8. Because we are not accelerating the object upwards in a true sense, we are just opposing gravity to lift the object. 9. $P = {W \over t}$

32. anonymous

thank you so much for your help ! i appreciate it !