What Is the Car's Acceleration Given These Forces?

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Homework Help Overview

The problem involves a 1200 kg car traveling at 50 km/h, experiencing forces from air resistance, road friction, and the force exerted by the wheels. The original poster attempts to calculate the car's acceleration using the equation a = ƩF/m, but expresses uncertainty regarding the application of the speed variable in their calculations.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants question the original poster's calculation of the net force and the interpretation of forces as vectors. There is discussion about the direction of forces and the relevance of the speed variable in the context of the problem.

Discussion Status

The discussion is ongoing, with participants providing feedback on the original poster's approach and encouraging a reconsideration of the force directions and the one-dimensional nature of the problem. Some guidance has been offered regarding the interpretation of forces.

Contextual Notes

There is mention of the original poster's recent start in the unit on forces, indicating a potential gap in understanding that may affect their approach to the problem.

harujina
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Homework Statement



A 1200 kg car travels at 50 km/h and experiences air resistance of 5000 N and road friction of 2200 N. If the wheels push with a force of 7500 N, what is the car's acceleration?

Homework Equations



a = ƩF/m

The Attempt at a Solution



I got ƩF = 8590 N [E52°S] then plugged it into the equation,
but it did not work to the correct answer of 0.250m/s^2.

I'm thinking I probably had to make use of the 50 km/h variable somewhere, which I didn't.
When and where would that apply...?
 
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harujina said:
I got ƩF = 8590 N [E52°S] then plugged it into the equation,
How did you find that sum? Realize that the forces point in different directions. Where did that angle come from?
 
how did you get ƩF=8590 [E52°S]?

To me it seems you interpreted it wrong. Its a one dimensional problem, but by the looks of your answer it is a vector result.

car is being pushed forward by 7500 N...backwards by air resistance of 5000 N...again backwards by road friction of 2200 N.

ƩF=ma

try again you should arrive at the right answer.

P.S. - No offense, but please consider revising the key points of the chapter associated with Forces.

Edit : Doc Al got there first!
 
ohh, okay i don't know why i thought air friction was in the direction north.
but thank you and yes, i just started this unit yesterday, i will make sure to revise!
 
harujina said:
ohh, okay i don't know why i thought air friction was in the direction north.
but thank you and yes, i just started this unit yesterday, i will make sure to revise!

great, glad you appreciate the help!:smile:
 

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