What is the mistake in my car's acceleration calculation?

[davedays]

Homework Statement

A car of mass 500kg climbs a 15 deg. hill. If the car's engine provides a forward thrust of 8000 N and the drag and friction on the car add up to 800 N calculate the car's rate of acceleration

Homework Equations

F=ma
Normal F= mg x 15 deg

The Attempt at a Solution

Normal force = mg x cos 15

NF = 500 x 10 x 0.9

NF = 4500 N

Backward Force = 800 + mg x sin15

BF = 800 +5000 x 0.2

BF=1800 N

Fwd Force = 8000 N

Resultant force = 8000 N - 1800 = 7200 N


F=ma

7200 = 500 x a
500a=7200
a= 14 ms

I have been killing myself and I still can't find the mistake !

Help me! please !

Thanks,

dave

 

[davedays]

Can someone please help me ?

 

[Tzim]

What add up to 800 mean?I don't think it means that friction is 800N

 

[Tzim]

Maybe that is the error.

 

[davedays]

No mate I just checked twice with the textbook that's exactly ow the question looks like.

 

[Tzim]

I don't said that the error was what the textbook said.i said that maybe you have misunderstood it.maybe it doesnot mean that T=800N

 

[davedays]

I think the mistake is somewhere in the resultant force and then there is a follow through :(

 

[Tzim]

It says drag nad friction add up to 800

 

[davedays]

so backward force is just 800 ?

 

[Tzim]

It cannot because only backward from weight is above 1000.But it may mean that friction is 800 less or more.I donnot know but the mistake must be there