Expression for the force on a particle

[Nightrider55]

Homework Statement

A particle of mass m is at rest at t=0. Its momentum for t>0 is given by Px=6t^2 kg m/s, where t is in s. Find an expression for Fx(t), the force exerted on the particle as a function of time.

Homework Equations

Px=MVx

The Attempt at a Solution

The question seems really simple but momentum confuses me. I know that momentum is related to the area under the Fx(t)curve between Ti and Tf by Pfx-Pix or the change in momentum, but I don't know where to go from there. Something to get me headed in the right direction would be greatly appreciated!

 

[cepheid]

Hint: Newton's second law states that:

$$\vec{F} = \frac{d \vec{p}}{dt}$$

 

[Nightrider55]

so then it would be F=12t. That seems a little too easy. When they say Px would I also have to find Py in order to find the mag of P?

 

[cepheid]

so then it would be F=12t. That seems a little too easy.

Maybe it is. What level of physics are you taking? Is it calculus-based? It's clear that you already know how to differentiate. If your prof expected you to be familar with calculus and to be aware that F = dp/dt was the true (most general) form of Newton's law, then yes, he has assigned a trivial problem. However, if you prof did not expect you to be familiar with calculus or F = dp/dt, then maybe he thought he had given you a stumper.

By the way, WERE you aware that F = dp/dt before I told you? If not, can you see that F = ma follows from this relation provided the mass of the particle is constant?

When they say Px would I also have to find Py in order to find the mag of P?

No. Why would you? They don't ask you for P or P_y. They only ask for P_x.

 

[Nightrider55]

Maybe it is. What level of physics are you taking? Is it calculus-based? It's clear that you already know how to differentiate. If your prof expected you to be familar with calculus and to be aware that F = dp/dt was the true (most general) form of Newton's law, then yes, he has assigned a trivial problem. However, if you prof did not expect you to be familiar with calculus or F = dp/dt, then maybe he thought he had given you a stumper.

By the way, WERE you aware that F = dp/dt before I told you? If not, can you see that F = ma follows from this relation provided the mass of the particle is constant?



No. Why would you? They don't ask you for P or P_y. They only ask for P_x.

I am in calculus physics and I talked to my teacher and he didn't realize that he assigned such an easy problem

I was aware that F = dp/dt before you told me but I didn't use it because I thought I was missing something because it seemed too simple of a problem considering it was among the more difficult problems at the end of the chapter.