# college physics

a) A light-rail commuter train accelerates at a rate of 1.25 m/s2. How long does it take it to reach its top speed of 80.0 km/h starting from rest?

(b) The same train ordinarily decelerates at a rate of 1.75 m/s2. How long does it take to come to a stop from its top speed?

(c) In emergencies the train can decelerate more rapidly, coming to rest from 80.0 km/h in 8.30 s. What is its emergency deceleration in m/s2?

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1. V = 80km/h = 80000m/3600s = 22.22 m/s.

a. V = Vo + a*t = 22.22 m/s.
0 + 1.25t = 22.22. Solve for t.

b. V = Vo + a*t = 0
22.22 - 1.75*t = 0. Solve for t.

c. V = Vo + a*t = 0
22.22 + a*8.30 = 0. Solve for a; it
should be negative.

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posted by Henry
2. 17.776

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posted by jessica
3. 12

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4. V = 80km/h = 80000m/3600s = 22.22 m/s.

a. V = Vo + a*t = 22.22 m/s.
0 + 1.25t = 22.22. Solve for t.

b. V = Vo + a*t = 0
22.22 - 1.75*t = 0. Solve for t.

c. V = Vo + a*t = 0
22.22 + a*8.30 = 0. Solve for a; it
should be negative

1. 👍 0
2. 👎 0

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