1. The problem statement, all variables and given/known data A car weighing 1500kg traveling at 20m/s brakes, and takes 50m to stop. Part A) Calculate the work done Part B) Calculate the power needed to stop the car Known starting variables are.. u=20 v=0 s=50 m=1500 2. Relevant equations P=Fv W=Fs F=ma s=1/2(u+v)t v=u+at 3. The attempt at a solution Part A: To find the work done I think I have to find out the force of the car going forward, and to find that out, I think I need to know the cars retardation (F=ma) first. To find the retardation I used the motion equation below to find the time it took to stop. s=1/2(u+v)t 50=0.5x20xt 50=10xt t=5 So the time it took to stop is 5s. Now I know the time, i used the motion equation below to find the retardation. v=u+at 0=20+(ax5) a=-20/5 a=-4 So the cars retardation is 4m/s^2. Now I can find out the force going forward by using F=ma F=ma F=1500x4 F=6000 So the force going forward is 6000N So therefore the work done is 6000x50 = 300000J ? Part B: Now I have worked out the power needed to stop the car two ways and I dont know which, if either, is correct. The first way i just did work done divided by time it took to stop. 300000/5 = 60000W But the second way I done it was force going forward times velocity. 6000x20 = 120000W Please help, my head hurts!