Material strain and stress

Question

A car starts from rest and accelerates at 1.5m/s2 until it reaches at 20km/hand stays at that speed for 5 minutes, it then accelerates at1m/s2 until it reaches 40km/h. It stays at that speed for 15minutes and then decelerates at2.5m/s2 until it is brought to rest 

a) the time taken

b) the total distance travelled

Answer 1

There are five parts to this motion; converting 1 km/hr = 1000/3600 = 0.278 m/s

 

1. x1 = (v² - u²)/2a = (20*0.278-0)²/2*1.5 = 10.29 m                         (accelerated motion)

 

2. x2 = velocity*time = 20*0.278*300 = 1668 m                                  (constant velocity)

 

3.  x3 = (v² - u²)/2a = ((40*0.278)² - (20*0.278)²)/2*1 = 46.37 m        (accelerated motion)

 

4. x4 = 40*0.278 * 15*60 = 10,008 m                                                 (constant velocity)

 

5. x5 = (40*0.278 - 0)²/2*2.5 = 24.7 m                                               (decelerated motion)

 

Total distance = x1+x2+x3+x4+x5 = 11,757.4 m = 11.7574 km