How Do You Calculate Acceleration and Distance in One Dimensional Motion?

[Teenytiny1991]

Homework Statement

A car accelerates uniformly from rest to a speed of 40 mi/h in 12.0 secs find A) the distance the car traveled during this time and B) the constant accelaration of the car

Homework Equations

a) Displacement of an object as a function of time: delta x =1/2(v0+v)T
B) Velocity as a function of discplacment = v^2= v0^2 + 2a delta x

The Attempt at a Solution

A) delta x = 1/2(0 + 20 m/s) 12
answer for part a = delta x = distance =120 m is this right?

B)(20 m/s)^2= 0^2 + 2a(120m)
400 m^2/s^2= 240ma
cross cancellation = answer for part b constant accelaration= 1.666666667= approx 2 m/s^2
Is this right?

 

[merryjman]

Your equations are right, but your conversion from mph to m/s is not quite correct. It's not exactly half, it's more like 0.447

 

[Teenytiny1991]

I'm sorry, what do you mean.

40 mi/h x 1h/60min x 1min/60 sec x 1609m/ 1 mi = 17.87777778 m/s but since there is only one sig fig i rounded it up to twnety. is that not how i should have gone about converting it?

 

[merryjman]

No, you did the conversion correctly, but you shouldn't worry about sig figs until the very end. Keep the 17.88 and then round when you're done. If your teacher told you otherwise, then your answer is right and you're done :)