# Homework Help: Help on Physics

1. Jun 25, 2006

### Musicman

The acceleration of a motorcycle is given by ax(t) = At - Bt2, where A = 1.70 m/s3 and B = 0.170 m/s4. The motorcycle is at rest at the origin at time t = 0.

(a) Find its position as a function of time t.

Find its velocity as a function of time t.

b. Calculate the max velocity it attains. I already calculated the max velocity it attains which is 28.33 m/s.

2. Jun 25, 2006

### Hootenanny

Staff Emeritus
Hi there musicman and welcome to PF,

What are your thoughts on this question? Would you mind posting what you have attempted thus far?

3. Jun 25, 2006

### Mindscrape

For the first question it looks like you are just supposed to integrate and sketch some graphs, but, as Hootenanny has already asked, what have you done so far?

4. Jun 25, 2006

### Musicman

ok i got:

v - v' = integral(At - Bt^2)dt
v = (1/2)At^2 - (1/3)Bt^3 + v'

x - x' = integral( v dt )
x = (1/6)At^3 - (1/12)Bt^4 + v't + x'

5. Jun 25, 2006

### Hootenanny

Staff Emeritus
That's correct, as the motocycle starts from rest your v' or constant of integration drops out.
This is also correct, again as your motocycle begins from rest at the origin your terms v' and x' drop out.

6. Jun 25, 2006

### Musicman

so would i write those exact functions in the space provided? or solve for an answer? and do i leave the apostrophes after the variables or no

7. Jun 25, 2006

### Hootenanny

Staff Emeritus
Well, they can be simplified a bit, but will your tutor accept unsimplified answers? As a said before, the v', v't and x' terms drop out because of the intial conditions imposed by the question;

8. Jun 25, 2006

### Musicman

yea, they gotta be simplified, thanks for the help.

9. Jun 25, 2006

### Hootenanny

Staff Emeritus
Have you attempted to simplify them? How are you getting on with your second question?

10. Jun 25, 2006

### Musicman

v = (1/2)At^2 - (1/3)Bt^3 + v' was this the one as position as a function of time or velocity? the velocity right? because x is displacement

11. Jun 25, 2006

### Hootenanny

Staff Emeritus
This is a function of velocity, this is a result of integrating acceleration.

12. Jun 25, 2006

### Musicman

ok right after it says find its velocity as a funtion of time it says (m/s) after the blank, so are they askign for a number or just the equation v=(1/2)At^2-(1/3)Bt^3...and isnt it ok for me to take off the +v' sicne it is zero?

13. Jun 25, 2006

### Hootenanny

Staff Emeritus
Is a function a number of an equation?
Yes, in fact you should do as I have said on numerous occasions previously.

14. Jun 25, 2006

### Musicman

i wrote an actual number for position as a function of time and velocity as a function of time and got it wrong

15. Jun 25, 2006

### Hootenanny

Staff Emeritus
Damn webassign homework :grumpy: . Sorry, I'm not getting at you. What exactly did you write?

16. Jun 25, 2006

### Musicman

13.12 m for the position as a fucntion of time and 17.34 m/s as the velocity as a function of time.

17. Jun 25, 2006

### Hootenanny

Staff Emeritus
Where did you get those numbers from? There is no way you can calculate them; besides the question asks for a function, not a numerical answer.