# Homework Help: Accelation problem, how do I change units (km/h to m/s)?

1. Aug 22, 2009

### pillar

I made a mistake I meant km/h to m/s^2.
1. ThrustSSC, the world's first supersonic car, accelerates from rest to 1000km/h in 16 s. What is its acceleration in m/s?

2.a=v/t = v-v0/t-0

3. I'm not sure how to change units (Professor didn't show me.), so can you please now all the work to the problem? Thanks in advance.

Last edited: Aug 22, 2009
2. Aug 22, 2009

### Pengwuino

Use dimensional analysis, first you should convert the speed from km/h to m/s. Whats the conversion between kilometers and meters? And hours to seconds? The first is easy, 1000m = 1km. The second is 1h = 3600s. Simply multiply the speed by the correct conversion factors to get your result.

3. Aug 22, 2009

### pillar

Re: Accelation problem, how do I change units (km/h to m/s^2)?

Wait I'm sorry I meant km/h m/s2.

4. Aug 22, 2009

### Staff: Mentor

Re: Accelation problem, how do I change units (km/h to m/s^2)?

Do as Pengwuino says: First convert km/h to m/s.

Hint: 1 km = how many meters? 1 hr = how many seconds? Substitute!

5. Aug 22, 2009

### pillar

Re: Accelation problem, how do I change units (km/h to m/s^2)?

1 km=1000m 1 hr = 3600s I'm not sure how to convert it to m/s^2 Unless I'm suppose to square the 3600, right?

6. Aug 22, 2009

### ideasrule

Re: Accelation problem, how do I change units (km/h to m/s^2)?

So this guy accelerated by 1000km/h in 16 s. That's 62.5 km/h every second. What's 62.5 km/h in m/s?

7. Aug 22, 2009

### Pengwuino

You don't want to divide by the time it took him to reach that speed in the first step. If you did, you'd have something with units km/(h*s) which isn't what you want. Put your answer into m/s and then you can divide by the time in seconds which will result in a m/s^2 answer. Fill in the blanks here:

$$$\frac{m}{s} = \frac{{km}}{h}*\frac{{1h}}{{?s}}*\frac{{?m}}{{1km}}$$$

8. Aug 30, 2009

### pillar

I understand now velocity is m/s, plugging it into a formula (say acceleration = change in velocity/time) time=s velocity= m * s^-1 m * s^-1 * s^-1=m/s^-2=m/s^2

Thanks all.