Find the total displacement and total distance traveled.Find your average speed and average velocity in meters/min.Find your average speed and average velocity in meters/sec.

Question

On a bright sunny day you decide to take a walk. You begin at your home and walk 1000 meters to an ice cream shop in 10 minutes. You spend 15 minutes ordering your ice cream and then return home. Since you have an ice cream cone in your hand, it takes 20 minutes to walk home.

1. Find the total displacement and total distance traveled.

2. Find your average speed and average velocity in meters/min.

3. Find your average speed and average velocity in meters/sec.

Answer 1

1) Starting at home and returning to home gives a displacement of zero and distance of 2,000 m.

2) Average speed = distance/total time = 2,000 m/ 45 min = 44.44 m/min. Average velocity = displacement/total time = 0.

3) Average speed = (44.44 m/min) * (1 min/60 s) = 0.7407 m/s. Average velocity is still zero.

Answer 2

Let’s first learn how to read and parse a question.

“On a bright sunny day you decide to take a walk. You begin at your home and walk 1000 meters to an ice cream shop in 10 minutes. You spend 15 minutes ordering your ice cream and then return home. Since you have an ice cream cone in your hand, it takes 20 minutes to walk home.”

becomes shorter when you keep only

the important stuff

On a bright sunny day you decide to take a walk. You begin at your home and walk 1000 meters to an ice cream shop in 10 minutes. You spend 15 minutes ordering your ice cream and then return home. Since you have an ice cream cone in your hand, it takes 20 minutes to walk home.

... now looks like a list of facts:

1. 1000 meters
2. 10 minutes
3. 15 minutes
4. “return home” -> 1000m
5. 20 minutes

For average quantities recall we only care about totals.

Now is when you start calculating relevant totals just because you can. The total time is (10 + 15 + 20)min = 45min. Total distance is 1000 twice = 2000m; but since you returned home, where you started in the first place, the total displacement is zero.

let’s answer the questions now

1. Find the total displacement and total distance traveled.

already got that. nice

2. Find your average speed and average velocity in meters/min.

Go to the definition of avg speed. It’s total distance over time so 2000m/45min = ...

We already know avg velocity is zero. We know this because we ended where we began in space, and we just have to realize this is a very typical situation you just can simply know about. If you end where you start, the vector displacement - which is defined as an arrow pointing from your starting position to your final - is naturally the zero vector. Just know it.

3. Find your average speed and average velocity in meters/sec.

This is a unit conversion. If you cannot complete this step, it’s a red flag that you need to backtrack and learn the previous curriculum. Physics is nothing if not relentlessly cumulative. Go back and learn what you missed now before you are too far gone.