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 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
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
4K
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