# Homework Help: Motion: Solving problems using equations

1. Sep 19, 2009

### tryintosurviv

Im sorry if this is in the wrong area ! and I know that this is the easiest question in the history of physics but I need help. I think some of the answers in the back of the text are wrong but I might be just the biggest idiot on the face of the earth so feel free to point that out. anyways .....1. The problem statement, all variables and given/known data
If 100m sprinters accelerate from rest for 3.5 s at 2.8 m/s (squared) , how far have they ran to this point ? How long will it take them to complete the 100m sprint , assuming they maintain their speed the rest of the way ?
2. Relevant equations

d= v1t + 1/2a t (squared)

I think ?

3. The attempt at a solution

= 3.5 + 1/2 (2.8)(3.5) squared
= 3.5 + 1/2 (2.8)(12.3)
=3.5 + 34.2 divided by 2
= 3.5 + 17.2
= 20.7 sorry I don't have the division sign or superscript

and I can't do the rest of the question without having the first answer correct. The text says the answer is 17 m

2. Sep 19, 2009

### Staff: Mentor

Hint: What's the initial speed? (What you call v1.)

3. Sep 19, 2009

### tryintosurviv

Isn't it 0 m/s ? It says from rest

4. Sep 19, 2009

### Staff: Mentor

Exactly! Do you see what's wrong with your calculation now?

5. Sep 19, 2009

### tryintosurviv

OH wow thats great. I was adding instead of multiplying ! Thanks