What is the Average Speed and Acceleration of a Car on a Straight Road?

[Tonia]

It would be the same?

 

[haruspex]

Would the expression for speed be: v = m = (45 mi/hr - 0 mi/hr)/2.5 sec. = 18 mi/hr/sec.??

No, that's calculating an acceleration, not a speed.
Write out the general equation that relates speed, time and (uniform) acceleration.
You have a value for the acceleration, and a value for the speed, and we're leaving the time as an unknown t. Plug those into the equation.

 

[haruspex]

It would be the same?

What would be the same as what?

Edit: Ok, you were replying to this:
Right, so how would the average height (=average speed) compare with the height half way along (=instantaneous speed at half time)?

Yes.
(Please use the Reply button or the quote button so people know what you are answering.)

 

[Tonia]

The equation would be Vf = Vo + at??

 

[haruspex]

The equation would be Vf = Vo + at??

Right, so plug in the values for v₀, v_f and a that are appropriate to question d).

 

[Tonia]

45 mi/hr = 0 + 9 mi/hr/sec times t
Solve for t??

 

[Tonia]

t would be 5.

 

[haruspex]

45 mi/hr = 0 + 9 mi/hr/sec times t
Solve for t??

What was the speed you calculated in part a)?

 

[Tonia]

22.5 mi/hr

 

[haruspex]

22.5 mi/hr

Right. That is the speed you are told to use in answering part d).

 

[Tonia]

so t is 2.5 seconds and that's the answer to d.

 

[haruspex]

so t is 2.5 seconds and that's the answer to d.

Yes.

 

[Tonia]

Okay. thanks for your help!

 

[Tonia]

Let me ask you one more question just to make sure: for problems a) and c), the answer is the same? 22.5mi/hr??

 

[haruspex]

Let me ask you one more question just to make sure: for problems a) and c), the answer is the same? 22.5mi/hr??

Yes.

 

[Tonia]

Okay, thanks!