How Do You Calculate Average Speed in Different Driving Conditions?

[hiineko]

Homework Statement

You drive on Interstate 10 from San Antonio to Houston, half the time at 58 km/h and the other half at 103 km/h. On the way back you travel half the distance at 58 km/h and the other half at 103 km/h. What is your average speed (a) from San Antonio to Houston, (b) from Houston back to San Antonio, and (c) for the entire trip? (d) What is your average velocity for the entire trip?

Homework Equations

V=d/t[/B]

The Attempt at a Solution

with a help of a friend online but I still don't understand it.
a.) (58*t/2 + 103*t/2) / t = 58/2+103/2 = (58+103)/2 = 80.5 The problem is I don't know how did "t" gone
b.) D/(D/2/(58))+(D/2/(103)) = ??
c.) none, stuck in A and B so can't answer this
d.) I don't why "zero" is the answer here pls explain

Help pls
I kinda suck at Algebra which lead to sucking in Physics too lol

 

[Robin04]

a.) (58*t/2 + 103*t/2) / t = 58/2+103/2 = (58+103)/2 = 80.5 The problem is I don't know how did "t" gone

If it hadn't gone, you couldn't have solved the equation because you have no information about the duration of the trip.

b.) D/(D/2/(58))+(D/2/(103)) = ??

What is the problem here? This equation is correct, you just have to solve it.

c.) none stuck

You have to use the same equation: v=d/t. What is the distance and time if we look at the entire trip? As you don't have exact data about these, you have to express them somehow and hope that the unknown cancels :D.

d.) I don't why "zero" is the answer here pls explain

What is the difference between speed and velocity?

 

[Qwertywerty]

The Attempt at a Solution

with a help of a friend online but I still don't understand it.
a.) (58*t/2 + 103*t/2) / t = 58/2+103/2 = (58+103)/2 = 80.5 The problem is I don't know how did "t" gone
b.) D/(D/2/(58))+(D/2/(103)) = ??
c.) none stuck
d.) I don't why "zero" is the answer here pls explain

Help pls
I kinda suck at Algebra which lead to sucking in Physics too lol

Do you know what average speed and velocity is ? What exactly is your doubt ? What do you mean by none stuck ?

 

[hiineko]

Do you know what average speed and velocity is ? What exactly is your doubt ? What do you mean by none stuck ?

Sorry I meant to say no answer because I got stuck to letter a and b.

my doubt is I'm lacking knowledge of doing it algebraically.
especially in letter A I mean how did t has cancel or eliminated

 

[hiineko]

If it hadn't gone, you couldn't have solved the equation because you have no information about the duration of the trip.What is the problem here? This equation is correct, you just have to solve it.You have to use the same equation: v=d/t. What is the distance and time if we look at the entire trip? As you don't have exact data about these, you have to express them somehow and hope that the unknown cancels :D.What is the difference between speed and velocity?

Letter A. So can you explain how did "t" got cancel or eliminated
Letter B. Can you lend me a hand of doing it?
Letter C. I'll deal with later because I need the answer of A and B to answer this
Letter D. Hmmm none?

 

[Qwertywerty]

Average speed is defined as the distance traveled in some particular time . Often , when you move , your speed is not constant , and tends to change . So we define average speed , to refer to the average distance traveled per unit time .

Post edited .

 

[Qwertywerty]

Part D - Average velocity is net displacement ( in a certain time interval ) upon time interval considered . What is net diplacement when you leave SA , and then come back to SA ?

Part C , involves some calculation .

Hope this helps .

 

[hiineko]

Part D - Average velocity is net displacement ( in a certain time interval ) upon time interval considered . What is net diplacement when you leave SA , and then come back to SA ?

Part C , involves some calculation .

Hope this helps .

Okayy I got letter D thankyou!
Sir problem is I can't do it algebraically especially A look the first post above, I don't know how t got cancel.

 

[Qwertywerty]

Sir problem is I can't do it algebraically especially A look the first post above, I don't know how t got cancel

Ok , yes I had made a mistake in my earlier post .
Corrected - let time taken to reach H be t . First half , with speed v₁ and second half with v₂ .

So , for t/2 , car ( I assume ) travels a distance v₁*t/2 , and the second t/2 , v₂*t/2 .
So total distance traveled is equal to v₁*t/2 + v₂*t/2 = ( v₁/2 + v₂/2 )*t ←taking t out common .

Now , average speed = ( v₁/2 + v₂/2 )*t/t ←formula of average speed .
Can you now cancel t ?

I hope this is clear enough . If not , feel free to ask what is not .

 

[hiineko]

Ok , yes I had made a mistake in my earlier post .
Corrected - let time taken to reach H be t . First half , with speed v₁ and second half with v₂ .

So , for t/2 , car ( I assume ) travels a distance v₁*t/2 , and the second t/2 , v₂*t/2 .
So total distance traveled is equal to v₁*t/2 + v₂*t/2 = ( v₁/2 + v₂/2 )*t ←taking t out common .

Now , average speed = ( v₁/2 + v₂/2 )*t/t ←formula of average speed .
Can you now cancel t ?

I hope this is clear enough . If not , feel free to ask what is not .

Wow thankyou! That was so clear. Thankyou thankyou! I'll update you again if I have more questions. Good day sir