Racing Car's Avg Speed: Find the Answer!

[iamchattha]

Homework Statement

A racing car accelerates uniformly through three gears, changes with the following average speed
20 for 2.0 s
40 for 2.0 s
60 for 6.0 s
what is the overall average speed of the car?
a) 12
b) 13.3
c) 40
d) 48
e) 37

Homework Equations

The Attempt at a Solution

 

[Doc Al]

Well? Where's your attempt?

 

[iamchattha]

Well? Where's your attempt?

could not think of a possible formula.

 

[Doc Al]

What's the most basic definition of average speed?

 

[iamchattha]

What's the most basic definition of average speed?

distance traveled by an object during an interval

 

[William White]

could not think of a possible formula.

err, everybody in the whole world knows that

speed = miles per hour (or km per hour)

so you know one formula!

 

[iamchattha]

err, everybody in the whole world knows that

speed = miles per hour (or km per hour)

so you know one formula!

but in the case of above mentioned question three speeds and vales of time are give...not distance and time...i have to drive average speed using 3 vales of speed and time

 

[William White]

okay
you are in a car that goes 20 miles per hour for 2 hours; then 40 miles per hour for 2 hours and then 60 miles an hour for 6 hours.

how long has elapsed (in hours) and how far has the car gone (in miles) ?

 

[iamchattha]

could it be done in a way that i first find out 3 values of distance( x= vt) using the above data and then taking 10 s as total time I find average speed?

 

[William White]

Q1) a car travels at 20mph for 2 hours. How far has it gone?

 

[iamchattha]

okay
you are in a car that goes 20 miles per hour for 2 hours; then 40 miles per hour for 2 hours and then 60 miles an hour for 6 hours.

how long has elapsed (in hours) and how far has the car gone (in miles) ?

Q1) a car travels 20mph for 2 hours. How far has it gone?

40 miles

 

[iamchattha]

40 miles

it would be 480 miles in total

 

[William White]

edit, you know how to do it now.

 

[iamchattha]

edit, you know how to do it now.

are you referring to this
"could it be done in a way that i first find out 3 values of distance( x= vt) using the above data and then taking 10 s as total time I find average speed?"

 

[William White]

I'm referring to the fact you now know the total distance and the total time so you know the speed.

Don't overcomplicate this!

 

[Doc Al]

distance traveled by an object during an interval

Exactly!

Just calculate the total distance traveled.