Newtons second law question help?

[TMJ]

A car of mass 1000kg is travelling along a straight horizontal road at a constant velocity of 20m/s. The car experiences a resistive force of 500N.
Calculate the deceleration of the car   

Is this correct   

  F-500=0,  F=500N 
F=ma   

  therefore, a=1000/500  =0.5m/s^2     
Because it is decelerating it will be -0.5m/s^2

[BasicAcid]

Yeah but I think you mean a = -500/1000 = -0.5 ms^-2
You can say the force is negative if you choose a positive direction as its initial speed and as it says 'a resistive force' it means a force in the opposite direction hence the negative sign infront of the 500.

These questions are ridiculously easy 2 mark questions on the exam... I don't know why VCAA includes questions like these.

[Guest]

Remember that since the first part of the question mentions that it is traveling at a "constant velocity" it means it has zero net force. Then it says that there is a resistive force of 500. The resistive force itself has to be negative for the driving force to be positive and thus give a zero net force. Now remember that deceleration is due to the resistive force. Therefore substitute the value for the resistive force (-500) into the equation.

F=ma
-500=1000*a
a=-500/1000
a=-0.5m/s^2

As it has always been said, getting the answer is not the point. It seems that you struggle in your thought process. Before substituting values into the equation, think about what is "physically" happening. Then you will be able to order your thoughts are result in clear processes. I know that it's probably late to reply to this thread as an answer has already been reached and provided for you. However, I think we can all benefit from orderly thought processes in the exam.

[BasicAcid]

Hey Emazing, look at the dates these threads were made.
And look at the date of the last poster (which was me nearly a month ago, how coincidental LOL).

There's no point replying to these threads cause I highly doubt the OP still needs your help a month after asking the question and not only that, the question was already answered.

I understand you're probably trying to reinforce your own understanding which is great. But you could always do that in your own head or even PM the OP.

Please stop though, thanks.

[Guest]

Understand. I'm not going to kill the thread.
Even though he may not benefit or need our help, others referring to this thread in the future won't go wrong. Of course, there is no point in replying to a thread which is ancient, but I think this only is fine.