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# I need help on some physics questions (kinematic equations)?

1. A starts with an initial velocity of 10m/s and decelerates at -2 m/s^2. After comes to a full stop, it accelerates with an acceleration of 2 m/s^2 until it reaches 20 m. What is the average velocity in the entire trip?

2. You are on a train. The train stops are spaced so that it takes the train 1.5 minutes to go between each stop. Because the train stops are so close together, the train never stops accelerating: As it leaves each stop it accelerates from stationary at +0.2m/s^2 until it hits its maximum velocity, then immediately starts to slow down at the same rate to return to stationary by the time it reaches the next stop. Assuming that the train travels in a straight line, how far apart are the stops in meters?

### 1 Answer

- oubaasLv 73 months ago
1)

t1 = (0-V1)/a1 = (0-10)/-2 = 5.0 sec

S1 = V1*t1/2 = 10*5/2 = 25 m

t2 = (V2-0)/a2 = 20/2 = 10.0 sec

S2 = V2*t2/2 = 20*10/2 = 100 m

Vav = (S1+S2)/(t1+t2) = 125/15 = 25/3 of m/sec (8.33)

2

d = 2*(a/2*(t/2)^2 = 2*0.1*(1.5*60/2)^2 = 405 m