What Is the Car's Acceleration Given These Forces?

[harujina]

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...?

 

[Doc Al]

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?

 

[NihalSh]

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!

 

[harujina]

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!

 

[NihalSh]

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!