Displacement & Average Velocity

AI Thread Summary
A car travels at 40 km/hr for 1 hour and 60 km/hr for 2 hours, resulting in a total distance of 160 km. The average velocity is calculated using the formula for average velocity, which is total displacement divided by total time. The total time for the journey is 3 hours. The confusion arises from mixing up units of speed and distance; the correct answer for distance should be in kilometers, not kilometers per hour. Understanding the distinction between average velocity and average speed is crucial for solving these types of problems.
Violagirl
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Homework Statement



A car travels in a straight line at 40 km/hr for 1 h and 60 km/hr for 2 h. A) How far does it travel? B) Find the average velocity.

Homework Equations



Average velocity = Δx/Δt (change in distance/change in time)


The Attempt at a Solution



In solving for A, I got (1 h x 40 m/hr + 2 h x 60 km/hr) = 160 km/hr

For B, this is where I'm confused. I know that if I try to arrange it as suggested in the formula (160 km/hr/2-1 h), wouldn't this just leave me with the remaining distance and eliminating the unit for time? Or would that be correct? I feel like it would not be though as the formula suggests, average velocity is defined by change in distance per change in time. Any help is greatly appreciated!
 
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The answer to A should have units of distance, not speed.
 
lewando said:
The answer to A should have units of distance, not speed.

Oh wow, I can't believe I missed that...Thanks a lot!
 
Violagirl said:

Homework Statement



A car travels in a straight line at 40 km/hr for 1 h and 60 km/hr for 2 h. A) How far does it travel? B) Find the average velocity.

Homework Equations



Average velocity = Δx/Δt (change in distance/change in time)
average velocity is total displacement divided by total time. The total distance divided by the total time is the average speed. Doesn't make any difference in this example, though.

The Attempt at a Solution



In solving for A, I got (1 h x 40 m/hr + 2 h x 60 km/hr) = 160 km/hr
right number, wrong units. You are solving for a distance.
For B, this is where I'm confused. I know that if I try to arrange it as suggested in the formula (160 km/hr/2-1 h), wouldn't this just leave me with the remaining distance and eliminating the unit for time? Or would that be correct? I feel like it would not be though as the formula suggests, average velocity is defined by change in distance per change in time. Any help is greatly appreciated!
check units! and welcome to PF!
 
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