Acceleration Disadvantage: Solving a Problem with a Go-Kart and Different Masses

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Homework Help Overview

The discussion revolves around a theoretical problem involving the acceleration of a go-kart with different masses and a specified engine power. The original poster seeks to understand the acceleration disadvantage when comparing an 80kg mass to a 65kg mass, with the go-kart's mass included in the calculations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the principles of force and acceleration, particularly the relationship defined by F=ma. There is exploration of how to derive force from power ratings and the implications of using kinetic energy in calculations. Some participants question the assumptions made regarding the engine's power output and its application to the problem.

Discussion Status

Participants are actively engaging with the problem, with some providing calculations and alternative approaches. There is recognition of the need to consider both the work done by the engine and the time taken to reach the desired speed. While some calculations have been presented, there is no explicit consensus on the final interpretation of the results.

Contextual Notes

Participants note the importance of making attempts at solving the problem before receiving assistance, and there is an emphasis on understanding the underlying physics principles rather than simply providing answers. The discussion includes considerations of unit conversions and the assumptions about the engine's performance.

oblit
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Hi Guys,

I'm a newbie to this, so be gentle!

I'm trying to work out a (simple, but I can't do it!) problem regarding a theoretical acceleration disadvantage...

What is the disadvantage in acceleration when a go-kart with a 7.5HP engine is used to propel a 80kg mass to 10m/s, when compared to a 65kg mass? (assume kart mass is 110kg).

Any help & workings would be most appreciated!

Thanks.
 
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Welcome to PF! You must make an attempt or discuss your ideas before you can receive any help on the forum. What principles do you think you need to answer this question.
 
Well, obviously F=ma is involved.

What I'm having difficulty with is calculating the "Force" of the engine from a power rating. This would be a lot easier question for me to solve if it was related to the thrust of a turbofan!
 
Horsepower is obviously a power rating. You might want to convert that to kilowatts. You can just type that into google and it will give you the conversion factor. Instantaneous power is force multiplied by velocity.
 
Okay, I've given it a go.

I calculate that to 10 m/s, the 80kg mass will accelerate at 2.9 m/s, while the 65kg mass will accelerate at 3.2 m/s, leaving a 0.3 m/s gap. This is assuming that I am correct in thinking that the motor will provide a forward force of 560N.
 
Ok probably got you to attack this from the wrong angle because I wasn't thinking about it properly. Power is also the rate of doing work and work is the change in kinetic energy. Since the kart is starting from rest the initial kinetic energy is 0. One can assume that the kart uses all its 7.5Hp to accelerate the kart from rest to its speed of 10m/s and find the time it takes to do that. Then one can work out the acceleration.
 
Right, 2nd attempt!

Work done by engine to accelerate 190kg total mass to 10 m/s = (190*10^2)/2 = 9500J

Work done by engine to accelerate 175kg total mass to 10 m/s = (175*10^2)/2 = 8500J

Using P=W/t & the total engine power as 5600W (can I do this?)

t for 190kg mass = 1.7 s (seems very fast!)
t for 175kg mass = 1.5 s (seems very fast!)


sooo...a 0.2s disadvantage to 10m/s?
 
That seems a better way of doing it. :approve:
 

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