# Dynamics problem

1. Oct 7, 2014

### phyziks4lyfe

• Warning! Posting template must be used for homework questions.
this is a part of a much bigger problem, I have a 600lb motorcycle going from point A to point B, which are 500 ft apart, i know the force exerted by the road on the motorcycle when the throttle is pressed is F(t)=300(1-.1t).
I need time in order velocity at B ,
I'm really lost on where to start on this, i was thinking f=ma could give me acceleration, but then i dont know what to do with that.

2. Oct 7, 2014

### paisiello2

Are you trying to determine the velocity at point B?

If you know the acceleration then by definition you should be able to get the velocity.

3. Oct 7, 2014

### phyziks4lyfe

so f=ma will give me a acceleration as a function of t, and yes i need velocity at B, but then won't i only have velocity as a function of t if by definition?.

4. Oct 7, 2014

### RUber

Right, but if you have velocity, you can find position. Find how long it takes to get to point B, then use that t for your velocity.

5. Oct 7, 2014

### SteamKing

Staff Emeritus
Gee, if only there were a way that acceleration could be used to get velocity, and that velocity could then be used to find distance. It would seem to be a good reason to study rectilinear motion in physics, or something. Maybe somebody wrote a textbook on how to do this stuff. IDK, that would probably take a lot of work to figure out.

6. Oct 7, 2014

### phyziks4lyfe

so would i use Vi^2=Vf^2+2A(500) and substitute in V and A as their function of t equations? because then i get t= 10.05 does that seem right?

7. Oct 7, 2014

### RUber

What units are you using for m, F, and distance? I hope F is in ft/lbs.

8. Oct 7, 2014

### phyziks4lyfe

m = slugs, F lbs, distance = ft

9. Oct 7, 2014

### haruspex

No, that formula only works for constant acceleration. You need to use the general relationships between acceleration, velocity, and distance - namely, integral formulas.
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