1. A world-class sprinter accelerates to his maximum speed in 4.0s. He maintains this speed for the remainder of the 100-m race, finishing with a time of 9.1 seconds. Find A] What is the runners average acceleration during the first 4.0 seconds. 2. Vx=Vox+AxT X=Xo+VoxT+1/2AxT Vx2=Vox2+2Ax(X-Xo) X-Xo=((Vox+Vx)/2)T 3. I used 100-m/9.1 seconds and got 10.99m/s as his average velocity. Divided it by 4 seconds to get an Acceleration of 2.75-m/s^2 but it is wrong. The correct answer is 3.5-m/s^2. Without knowing what distance he covered in the first 4 seconds I am stuck. Also, I've been having a little trouble understanding speed vs velocity how can average speed be different than average velocity? I read in my text that speed is the magnitude of velocity and that it cannot be zero. Also, that "speed denotes distance traveled divided by time..." Which is exactly what Velocity equals; so how can they be different?