Err, real easy problem but what'd he(or I) do wrong

  • Thread starter Thread starter schattenjaeger
  • Start date Start date
AI Thread Summary
The discussion revolves around calculating the necessary speed to achieve an average of 180 km/h over four laps after averaging 150 km/h for the first two laps. Initial assumptions led many to believe a speed of 210 km/h would suffice, but further analysis revealed that to meet the goal, a speed of 225 km/h is required for the final two laps. This conclusion is based on the time taken for each segment of the race, with the calculations showing that the average speed must compensate for the slower pace of the first half. The conversation highlights the complexity of average speed calculations and the common pitfalls in assumptions. Ultimately, the correct speed to achieve the desired average is confirmed to be 225 km/h.
schattenjaeger
Messages
176
Reaction score
0
the problem was that a guy wants to average a speed of 180 km/h while driving 4 laps around a race track.
after 2 laps, he's only averaged 150, so its asking what the average would have to be so that he does attain his goal.

So everybody would read the question, put 210, then check the answer in the back of the book and they would assume they are right.

But from the start i knew it wasnt what it seemed. Since If 1 lap=1 km, then going 180 km/h, it would take you 80 seconds to finish all 4 laps.

But, going 150, it would take you 48 seconds to finish 2 laps, and then going 210, it would take you roughly 35 seconds. which comes out to ~83 seconds, and not 80.

So The point is to find how fast you have to go to do a lap in 32, seconds, which comes out to 225 km/h.

When i first started explain it, no one would believe me, i felt like galileo or something


I got 210 myself, and upon close scrutinizing I can't find an error in either of our calculations, and all things considered, the inverse ability function probably made me wrong(what's the saying, you know you're a physics major when you can do vector calculus but don't remember long division?)
 
Physics news on Phys.org
You're correct. Can you read my working ?
 

Attachments

  • schatenjaegger.jpg
    schatenjaegger.jpg
    20.6 KB · Views: 500
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 .
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Thread 'A bead-mass oscillatory system problem'
I can't figure out how to find the velocity of the particle at 37 degrees. Basically the bead moves with velocity towards right let's call it v1. The particle moves with some velocity v2. In frame of the bead, the particle is performing circular motion. So v of particle wrt bead would be perpendicular to the string. But how would I find the velocity of particle in ground frame? I tried using vectors to figure it out and the angle is coming out to be extremely long. One equation is by work...
Back
Top