## MTALHAHASSAN2 one year ago Need help!! A car skids to a stop on a road with a uk of 1.1. If the intial speed of car is 50 km/h how many meters long are the skid marks.

1. Michele_Laino

here we have to keep in mind that the work done by the friction force has to be equal to the kinetic energy change, so we can write: $\Large {\mu _k}mgd = \frac{1}{2}m{v^2}$ where m is the mass of your car, and d is the requested distance. Furthermore g is the earth gravity, and v is the velocity of our car

2. MTALHAHASSAN2

|dw:1435905880197:dw|

3. MTALHAHASSAN2

|dw:1435905970542:dw|

4. MTALHAHASSAN2

|dw:1435906093552:dw|

5. MTALHAHASSAN2

I just covert 50 km/h in m/s

6. MTALHAHASSAN2

@Michele_Laino

7. MTALHAHASSAN2

|dw:1435906235486:dw|

8. MTALHAHASSAN2

Is i do it right

9. MTALHAHASSAN2

plz plz help me

10. IrishBoy123

you dropped g out of your calculation so you are out by a factor of about 10

11. MTALHAHASSAN2

@IrishBoy123 from which step

12. IrishBoy123

|dw:1435912438381:dw|

13. IrishBoy123

also, does 89m sound realistic?!

14. MTALHAHASSAN2

Idk i just get that answer

15. MTALHAHASSAN2

ut the answer at the back of my book is 8.64 m [F]

16. MTALHAHASSAN2

But*

17. IrishBoy123

i am referring to your answer given above - ie 89m. |dw:1435912972594:dw| i get $$\frac{50,000^2}{3600^2 \times 2 \times 1.1 \times 9.8} = 8.95m$$

18. MTALHAHASSAN2

|dw:1435912949019:dw|

19. IrishBoy123

are you finished?

20. MTALHAHASSAN2

I still don't get the answer