Why Did My Calculation of Driving Speed Result in an Error?

  • Thread starter Thread starter Manodesi524
  • Start date Start date
  • Tags Tags
    Velocity
AI Thread Summary
The discussion revolves around a calculation error in determining the average speed required for a car after jogging. The jogger calculated their jogging time and set up an equation to find the car's speed, resulting in an answer of 64 km/h, while the teacher indicated the correct speed is 50 km/h. The error stems from miscalculating the total time in the equation, specifically the value of x. Additionally, there's confusion regarding the use of miles instead of kilometers in the calculations. The correct approach involves recalculating the time based on the average speed formula to arrive at the accurate car speed.
Manodesi524
Messages
6
Reaction score
0

Homework Statement



You jog at 9.8 km/ h for 8.0 km, and then you jump in the car and drive an additional 16km. With what average speed must you drive the car if your avg speed for the entire 24 km is to be 22km/ h

Homework Equations


Average speed = distance/ time


The Attempt at a Solution



I found the time it took for my jog, which was approx. .84 miles.
Then I made an equation using some facts :

22= 24/ .84+ x

X is about .25 hours

So now that I know this I plug it into my equation that will solve the problem: 16/.25

My final answer is about 64 km/ hr.

My teacher says its 50. Where did I go wrong?
 
Physics news on Phys.org
You made an error calculating x. If 22 = 24 / (.84 + x), we know that the denominator for that equation must be equal to 24 / 22. Calculate that, then subtract .84 to get the time in the car. Then go from there.
 
Mark, i am sure x is .25. I've done the calculations several times. I would like an answer soon because today's test is modeled after the homework
 
Manodesi524 said:
I found the time it took for my jog, which was approx. .84 miles.
0.8163 hrs

My final answer is about 64 km/ hr.

My teacher says its 50. Where did I go wrong?
I say it's about midway between those values. Your method is correct, just need to retain more sig figs.
 
Manodesi524 said:

Homework Statement



You jog at 9.8 km/ h for 8.0 km, and then you jump in the car and drive an additional 16km. With what average speed must you drive the car if your avg speed for the entire 24 km is to be 22km/ h

Homework Equations


Average speed = distance/ time


The Attempt at a Solution



I found the time it took for my jog, which was approx. .84 miles.
Then I made an equation using some facts :

22= 24/ .84+ x

X is about .25 hours

So now that I know this I plug it into my equation that will solve the problem: 16/.25

My final answer is about 64 km/ hr.

My teacher says its 50. Where did I go wrong?
Why would you use miles to solve any part of this problem?
 

Thread 'Rolling without slipping on a curved surface'

Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
View full post »
Thread 'Voltmeter readings for this circuit with switches'

Thread 'Voltmeter readings for this circuit with switches'

TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
View full post »

Similar threads

Calculate the average speed and average velocity
Replies
2
Views
2K
Solve for Average Speed: Jogging and Driving Distance Calculation
Replies
1
Views
2K
How to calculate average velocity given distance and time?
Replies
6
Views
2K
Calculating Average Speed: Physics Homework Problem
Replies
13
Views
2K
What are the average speed formulas needed to solve this problem?
Replies
5
Views
5K
How to Calculate Average Velocity with Displacement & Speed?
Replies
3
Views
2K
I can't quite get this question.... (|Uav|)
Replies
8
Views
2K
What is the average speed for the entire trip?
Replies
2
Views
4K
How Fast Must You Drive to Average 22 km/h Over 24 km?
Replies
2
Views
2K
Checking Speed and Velocity Problems
Replies
2
Views
2K

Hot Threads

Recent Insights

Back
Top