# Homework Help: 1 d kinematics

1. Feb 1, 2009

### mppaki

1. why do the units for time appear twice in the units for acceleration
2. a = v/t - v1-vo/t1-t0
3. once for speed change and once for time change.

1. what is the acceleration of a car that travels in a straight line at a constant speed of 27 m/s?
2. 27m/s / 10s
3. 2.7m

2. Feb 1, 2009

### AEM

Is this:

1. why do the units for time appear twice in the units for acceleration

Is this:

2. a = v/t - v1-vo/t1-t0

It's not clear what you would like help with. Identify your question, then show your attempt to answer it.

3. Feb 1, 2009

### mppaki

a = v/t = v1-v0/t1-t0

i just want to know if i got the right answer or not

4. Feb 1, 2009

### glueball8

$$a=\frac{\Delta v}{\Delta t}= \frac{v_{f}-v_{o}}{t_{f}-t_{o}}$$

you can't write it like "v1-v0/t1-t0" this means that v1 minus (vo over t1) minus t0.

5. Feb 1, 2009

### mppaki

yeah thats the equation i thought would relate, but are my answer correct?

6. Feb 1, 2009

7. Feb 1, 2009

### mppaki

both number 1

8. Feb 2, 2009

### AEM

Okay, now that you have told us that Number 1 is the question in both cases, we can help you. First, your answer to question 1 is not correct. Think about the definitions. Velocity is change in position divided by change in time so the units are length/time or

$$V = \frac{L}{T}$$

Now acceleration is change in velocity divided by time. Take the equation I just wrote and do the algebra. What do you see?

For the second question. What is the adjective modifying the word speed??? What is the definition of velocity that I just wrote? Put those tow ideas together and what do you get?

Hint: With physics sometime it's useful to ask "What does it mean?" and then go back and look at the definitions.