# Can you verify my Physics work please?

• Feb 23rd 2013, 09:42 AM
sakonpure6
Can you verify my Physics work please?
I am preparing for a physics test and i want to make sure what and how I am solving the review questions is correct because I have no answer key!Thank you in advance!

2-You are driving in your car at a steady 80.0km/h. and you suddenly see a stop sign. You apply your breakes and stop after 60.0m(or 0.06km).

a)How long did it take you to stop?
What I did was find Vavg=0.5(80.0km/h + 0.0km/h) then using it in the equation of delta d=Vavg.*delta t and getting an answer of 0.0015h.

What I did was using the formula V2^2=V1^2+2a(delta d) and I solved to get a= (to appropriate sig fig) -53300km/h^2

3-During the span of 5.0s time intercal an object begins at 5.0m/s, accelerates uniformly and ends at 20.0m/s.

a) What is the average speed of the obect in this 5 s interval?
What I did Vavg=0.5(20.0m/s + 5.0m/s)=12.5m/s

b)What is the acceleration?
What I did v2=v1+2a(t)
20.0m/s=5.0m/s+2a(5.0s)
a= 3.0m/s^2

Thank you again!!
• Feb 23rd 2013, 03:17 PM
Cesc1
Re: Can you verify my Physics work please?

a=-4.11 m/s^2

t=5.4 s
• Feb 23rd 2013, 06:53 PM
sakonpure6
Re: Can you verify my Physics work please?
Quote:

Originally Posted by Cesc1

a=-4.11 m/s^2

t=5.4 s

I don't get what a= -4.11 m/s^2 and t= 5.4 are supposed to mean? Mind explaining them please.
• Feb 23rd 2013, 10:11 PM
Cesc1
Re: Can you verify my Physics work please?
Quote:

Originally Posted by sakonpure6
I don't get what a= -4.11 m/s^2 and t= 5.4 are supposed to mean? Mind explaining them please.

I just converted your answers from km/h^2 to m/s^2 and from hours to seconds because it is more conventional.