Average speed problem What am I missing?

Click For Summary

Homework Help Overview

The problem involves calculating the average speed of a person walking between two points at different speeds. The context is rooted in kinematics, specifically focusing on uniform motion and average speed calculations.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between distance, speed, and time, with some attempting to derive the average speed using the formula for average speed as total distance over total time. Others express confusion about calculating total time based on the given speeds.

Discussion Status

Some participants have provided guidance on how to approach the problem by suggesting the calculation of total time and total distance. There are indications of multiple interpretations regarding the manipulation of the equations involved, and some participants express confusion about the steps needed to arrive at the solution.

Contextual Notes

Participants note the lack of explicit values for distance and time, which may affect their ability to compute the average speed directly. There is also mention of the assumption of constant speed during the walks.

xXOfNiRXx
Messages
13
Reaction score
0

Homework Statement


A person walks from point a to point b at a speed of 5 m/s. Then she turns around and walks from point b to point a at a speed of 3 m/s. What is her average speed?


Homework Equations


Average speed is equal to d/ change in t.


The Attempt at a Solution


So I know the distance is 2d. I also know the acceleration is constant, though I don't know if I need it for the problem. So I tried to do 5m/s + 3m/s /2 to get the answer. That led to the wrong path. Since we don't have time, I'm assuming that maybe I use a kinematic equation. However, we don't know what acceleration is, other than it is constant.
 
Physics news on Phys.org
Here the person is walking with uniform velocity.
From a to b the time taken is t1 = d/5 m/s
From b to a the time taken is t2 = d/3 m/s
Find total time and total distance. Then the average velocity = total distance / total time.
 
I see that total distance is 2, or 2d. I am having trouble seeing how to get the time.
 
xXOfNiRXx said:
I see that total distance is 2, or 2d. I am having trouble seeing how to get the time.
Total time t = t1 + t1 = d/(5 m/s) + d/(3 m/s)
 
Tried working it out, but I'm not seeing it here. I see that by manipulation you get t=d/v at which point you plug in the speed that I am given. Can you explain a bit more. I'm quite confused here.
 
xXOfNiRXx said:
Tried working it out, but I'm not seeing it here. I see that by manipulation you get t=d/v at which point you plug in the speed that I am given. Can you explain a bit more. I'm quite confused here.
Average velocity = 2d/t = 2d/( d/5 + d/3)
 
Oooooooo! It all makes sense! Got it! Thanks so much! Really appreciate it. The trick was seeing that the d's would cancel! Thanks!
 

Similar threads

Average Speed Question for a Train that Accelerates and then Decelerates
  • · Replies 20 ·
Replies
20
Views
2K
Momentum: instantaneous or average?
  • · Replies 9 ·
Replies
9
Views
1K
Average speed and average velocity
  • · Replies 3 ·
Replies
3
Views
3K
Average speed with constant acceleration over a period of time
  • · Replies 7 ·
Replies
7
Views
2K
Finding time from average speed
  • · Replies 7 ·
Replies
7
Views
2K
Trying to get an average speed of 60 MPH
  • · Replies 8 ·
Replies
8
Views
4K
Why total time taken s₁/v₁ + s₂/v₂ + s₃/v₃ in average speed?
  • · Replies 46 ·
2
Replies
46
Views
4K
Calculate average speed/acceleration for the given function
  • · Replies 1 ·
Replies
1
Views
2K
Calculate Distance Traveled: Instantaneous vs. Average Velocity
  • · Replies 5 ·
Replies
5
Views
2K
What is the average speed for the entire duration? Trick?
  • · Replies 2 ·
Replies
2
Views
1K