How to calculate average velocity given distance and time?

  • #1

Homework Statement


A motorist drives north for 35.9min at 73.3km/hr and then stops for 15.4min. He then continues north, traveling 114.5km in 1.93hr. What is his average velocity?

Homework Equations


avg velocity = xf - xi / time

The Attempt at a Solution


35.9 min * (1 hr / 60 min) = 0.5983 hr
0.5983 hr * (73.3 km / hr) = 43 .858 km

total time = 0.5983 hr + 1.93 hr + 0.257 hr = 2.785 hr

avg velocity = xf - xi / time

= 114.5 km - 43.858 km / 2.785 hr

= 25.37 km /hr N

which is actually incorrect because the answer is meant to be 56.9 km /h N.
What am i doing wrong ?
 

Answers and Replies

  • #2
collinsmark
Homework Helper
Gold Member
2,923
1,332
avg velocity = xf - xi / time

= 114.5 km - 43.858 km / 2.785 hr
What is meant by "xf - xi" here, in general? And as applied to this problem?
 
  • #3
What is meant by "xf - xi" here, in general? And as applied to this problem?
the displacement and in this problem, the final distance and initial distance
 
  • #4
201
51
the displacement
That is where you have gone wrong I assume [itex]x_f[/itex] means final position and [itex]x_i[/itex] means initial position. Here 114.5 Km and 43.858 is already the displacement for the given time intervals. You can find the total displacement by adding the displacements.
 
  • #5
That is where you have gone wrong I assume [itex]x_f[/itex] means final position and [itex]x_i[/itex] means initial position. Here 114.5 Km and 43.858 is already the displacement for the given time intervals. You can find the total displacement by adding the displacements.
Wow thanks so much. If this question asked for average speed, would it be the same?
because i know avd speed = total distance / total time
 
  • #6
201
51
Wow thanks so much. If this question asked for average speed, would it be the same?
because i know avd speed = total distance / total time
Yes.
 
  • #7
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
35,588
6,453
Wow thanks so much. If this question asked for average speed, would it be the same?
because i know avd speed = total distance / total time
If all of the displacements are in the same direction, as they are here, average speed is the magnitude of the average velocity.
Since the question asks for average velocity, you should include the direction in the answer.
 
  • Like
Likes Mastermind01

Related Threads on How to calculate average velocity given distance and time?

  • Last Post
Replies
4
Views
2K
Replies
1
Views
3K
Replies
13
Views
633
Replies
1
Views
4K
Replies
2
Views
2K
  • Last Post
Replies
10
Views
3K
Replies
2
Views
1K
Replies
2
Views
6K
Top