- #1

physiman

- 13

- 0

Ok, now to business:

**A car with mass 600 kg accelerates uniformly from rest down a steady hill inclined at 15 degrees to the horizontal[...]**

- Work out the energy lost to friction after the car has travelled 100m

- The average frictional force acting on the car as it free-wheeled down the hill

- Work out the energy lost to friction after the car has travelled 100m

- The average frictional force acting on the car as it free-wheeled down the hill

**For the first 3 parts I had to work out the speed of the car after 100m in 20s, the KE after the car has travelled 100m and the GPE the car has lost after tavelling 100m down that slope. I got 10 ms^-1; 30 000 J and 152340.9 J respectively.**

**So I tried using the Work done formula to out the energy lost due to friction:**

W=Fd

For W I used the GPE the car has lost in PE, so 152340.9 J and got the value of F to be 1523.4 N. Is that the right method, I'm unsure because I think that I have to include the Kinetic Energy as well but the difference between KE and GPE looks too big for me.

Or do I have to use the F=ma formula? By that I mean work out a from the values I have, 0.5 m s^-2, and then I get 300N as the value for F but that doesn't look right to me as it has nothing to do with the energy loss.

well, I guess I can got to the next question only after I solve this one.

W=Fd

For W I used the GPE the car has lost in PE, so 152340.9 J and got the value of F to be 1523.4 N. Is that the right method, I'm unsure because I think that I have to include the Kinetic Energy as well but the difference between KE and GPE looks too big for me.

Or do I have to use the F=ma formula? By that I mean work out a from the values I have, 0.5 m s^-2, and then I get 300N as the value for F but that doesn't look right to me as it has nothing to do with the energy loss.

well, I guess I can got to the next question only after I solve this one.