# Homework Help: Newtons laws

1. Jan 8, 2014

### KiNGGeexD

I am a little stumped with this question:( I have attached my solution so far which has just been to deduce the acceleration on the flat surface

2. Jan 8, 2014

### KiNGGeexD

I posted images?

3. Jan 8, 2014

### Andrew Mason

Can you determine the time that the car takes to stop and the acceleration?

From that can you determine the co-efficient of kinetic friction?

Once you that you should be able to solve it.

AM

4. Jan 8, 2014

### KiNGGeexD

Ahh ok!
I determined the time to stop as 10 seconds and acceleration to be 0.3m/s^2:)

So how do I get the kinetic friction coefficient without the mass of the car?

5. Jan 9, 2014

### Andrew Mason

You should show us how you get that. What is the initial speed in m/s? Plot speed in m/s vs. time on a graph. What does the area under the graph represent? Work out the formula for that area and express in terms of change in speed and time.

Work it out using m for the car mass. You will see that mass cancels out.

AM

6. Jan 9, 2014

### CWatters

Write an equation, you might find the mass cancels.

7. Jan 9, 2014

### KiNGGeexD

I got

a= g(sinθ - μcosθ)

But it occurs to me I don't have the acceleration

8. Jan 9, 2014

### Andrew Mason

Determine the time it takes to stop. Your calculation of 10 seconds is wrong. How do you determine acceleration from the stopping time and initial velocity?

Show your work and we can help you. We cannot guess what you are doing if you just tell us what you "got".

AM

9. Jan 10, 2014

### KiNGGeexD

Ah I know what I have done wrong, I converted the initial speed into m/s incorrectly :)

I think I got it now