What Is the Average Speed of a Car on a Round Trip?

Click For Summary

Discussion Overview

The discussion revolves around calculating the average speed of a car on a round trip of 100 km, with a total time of 2 hours. Participants explore the distinction between average speed and average velocity, and clarify the correct equations to use in this context.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant states that the average velocity is zero because the car returns to its starting point, but questions the answer key which states the average speed is 50 km/hr.
  • Another participant clarifies that the problem is asking for average speed, not average velocity, and questions the correctness of the answer provided.
  • A participant acknowledges a mistake in writing the equation for average speed and attempts to correct it, but another participant critiques the revised equation as meaningless.
  • It is noted that the average speed can be calculated as total distance divided by elapsed time, leading to an average speed of 50 km/hr for the trip.
  • Participants discuss the difference between average speed and average velocity, emphasizing that the total displacement is zero while the total distance is 100 km.

Areas of Agreement / Disagreement

There is some agreement on the calculation of average speed as 50 km/hr, but confusion remains regarding the distinction between average speed and average velocity. Multiple viewpoints exist regarding the correct formulation of the equations involved.

Contextual Notes

Participants express uncertainty about the phrasing of the problem and the correctness of the answer key. There are unresolved issues regarding the definitions and applications of average speed versus average velocity.

huma
Messages
7
Reaction score
0

Homework Statement


a car starts from hither , goes 50km in a straight line to yon , immediately turns around, and turns to hither . the time for this round trip is 2 hours . the average speed of the car for this round trip is ?

Homework Equations



average velocity = disrance covered /time

The Attempt at a Solution


as the body comes back to its initial position so average velocity is zero ... but answer key shows the right answer is 50 km/hr ....I can't understand ... what you think what is correct answer
 
Last edited by a moderator:
Physics news on Phys.org
huma said:

Homework Statement


a car starts from hither , goes 50km in a straight line to yon , immediately turns around, and turns to hither . the time for this round trip is 2 hours . the average speed of the car for this round trip is ?

Homework Equations



average velocity = disrance covered /time

The Attempt at a Solution


as the body comes back to its initial position so average velocity is zero ... but answer key shows the right answer is 50 km/hr ....I can't understand ... what you think what is correct answer
It sounds like they are asking for average speed, not average velocity. Your equation you list is for average speed, not average velocity.

And 50km/hr looks to be a wrong answer, since the time elapsed is 2 hours. Are you sure you have written the problem and answer correctly?

EDIT -- I misread the problem, and now see why they got 50km/hr.
 
Last edited:
ohhhh yesh its my mistake I write wrong equation ...average speed = total speed /time ... what you think now my answer is correct or wrong ?
 
The car travels 100 km in 2 hr, so its average speed is 50 km/hr. But, as berkeman points out, the question asks for the average speed, not the average velocity.
 
huma said:
ohhhh yesh its my mistake I write wrong equation ...average speed = total speed /time ... what you think now my answer is correct or wrong ?
This equation -- average speed = total speed /time -- is meaningless (and wrong). There is no such thing as "total speed".
The corrected equation is speed = (total distance)/(elapsed time).
For velocitiy, it is velocity = (total displacement)/(elapsed time).
In your calculation, since the car started from and returned to the same point, the total displacement is 0, so the velocity is 0. That's not what they asked for, though.
 
  • Like
Likes   Reactions: Chestermiller

Similar threads

  • · Replies 9 ·
Replies
9
Views
1K
Replies
20
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
Replies
40
Views
7K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 10 ·
Replies
10
Views
5K
Replies
1
Views
2K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 14 ·
Replies
14
Views
3K
Replies
4
Views
9K