# HELP energy and work TROUBLE

1. Jul 20, 2004

### Physicshelpneeded

HELP!!! energy and work TROUBLE!!

....im very worried about my current lesson in class because it has me completely stumped!

Two objects move with different masses from rest and are pulled by the same magnitude net force and move through the same distance while the force acts on them. The work done on object 1 is 500 Joules (Nm). After the force has pulled each object, object 1 is moving twice as fast as object 2. Answer the following questions, showing your work.

(a) How much work is done on object 2? (i put the same amount, since the force and distance are the same in both, then work must be equal)

(b) What is the kinetic energy of object 1 AFTER being pulled? (this stumped me and i have no idea where to start)

(c) What is the kinetic energy of object 2 after being pulled? (i have no idea how to do c since b stumped me... )

(d) If the mass of object 1 is 20 kg, what is the mass of object 2?
(i put 20 kg for this answer, and i have no idea, nor formula, to show how i got it)

I NEED HELP!!! If u can help in ANY WAY please post a message for me! also, if u have useful links about this topic if u can post them i would really appreciate it!
THANKS!

2. Jul 20, 2004

### fisipavia

b) use the work-energy theorem: work = change in mechanical energy. Assuming that the objects are moved in an horizontal path (so there is no change in potential energy) then ... work = change in kinetic energy.
so kinetic energy = 500J
c) the same as b. kinetic energy is 500J
d) for object 1:
m= 20 kg, K = 500 J
use equation K = (1/2) mv^2
solve for v, this will give you the velocity for object 1. Since the problem says that object 1 is moving twice as fast as object 2.
then: velocity of object 2 = velocity of object 1 divided by 2

3. Jul 21, 2004

### JohnDubYa

The work in your equation is only that due to a nonconservative force. Gravity can do work on an object and not change the mechanical energy of the object.

4. Jul 21, 2004

### Physicshelpneeded

THANKS visipavia, that helped alot....thank u too john dubya