PHYSICS 100A QUIZ 1

FALL 2001 #85013

 

  1. A man runs 100m east with an average speed of 4m/s, after a while, he runs west 50m with the same average speed as shown in Fig. 1. Find the average velocity of the man during his motion.

 

 

 

 

 

 

 


                                   Fig 1 

 

 

 Solution. We select east as positive direction.

                 We find the time elapsed from

                       Dt = d/(average speed) = (100m + 50m)/(4m/s) = 37.5s

               

                  We find the displacement of the man from

                       Dx = x2 – x1 = 50m - 0m = 50m (east)

                  

                 We find the average velocity from

                       vaverage = Dx/Dt = (50m)/(37.5s) =  1.33m/s.

 

 Note that the direction of the average velocity is east.

 

 

 

 

 

 

 

  1. A car accelerates from rest to 60km/h in 8 seconds. What is the average acceleration of the car in m/s2 during this time interval?

 

Solution.  We find the average acceleration from

             

                        a = Dv/Dt = [(60km/h)(h/3600s) – 0 ]/(8s)

                           = 2.08m/s2