Change in the object's kinetic energy

1. Dec 14, 2004

UrbanXrisis

A force acting on an object given by the function F(x)=3x^2 + 4, where F is in Newtons and x is in meters. what is the change in the object's kinetic energy as it mores from x=1 to x=3 m?

W=6x
it changes from 6 J to 18 J
the answer 12 J is not the correct one
it says 26 J

why?

2. Dec 14, 2004

Parth Dave

Why is W = 6x?

3. Dec 14, 2004

UrbanXrisis

W=F’=∫P

F(x)=3x^2 + 4
F'(x)=6x

4. Dec 14, 2004

Pyrrhus

This is what i get

$$W = \int^{3}_{1} (3x^2 + 4)\vec{i} \cdot dx \vec{i}$$

$$W = x^3 + 4x]^{3}_{1} = 34 J$$

Work-Kinetic Energy Principle

$$\sum_{i=1}^{n} W_{i} = \Delta K$$

so

$$\Delta K = 34J$$

5. Dec 14, 2004

UrbanXrisis

that's not even one of the choices. Does it matter if it was F(x) instead of F(t)?

6. Dec 14, 2004

Parth Dave

Just so you know, i believe that 26 is wrong also.

EDIT*Looks like cyclovenom got there first. The 34 is correct.

Remember, W is not F', its the other way around.

F = W'

And yes it does matter if it was F(x) instead of F(t).

Last edited: Dec 14, 2004
7. Dec 14, 2004

UrbanXrisis

how would F be different if it was F(t)?

8. Dec 14, 2004

Pyrrhus

I am with Parth Dave, are you sure about this, urban?

9. Dec 14, 2004

UrbanXrisis

the packet must have a typo then

Cyclovenom, I never see you on ICQ :)

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