Question

5 13. If a train going 60 m/s hits the brakes, and it takes the train 2 minute 25 seconds to stop, what is the train's acceleration?​

Answer 1

Acceleration = -12/17 m/s ^2

Step-by-step explanation:

Name the variables

V = final velocity( velocity after the train stops) u= intial velocity(velocity when the train was moving at constant speed, before brakes are applied)

A = acceleration( in this case, it is deceleration)

T = time ( time taken to fully stop)

Second Step: What equation should we use?

The 3 Big Motion in One Dimension Formulas are:

V = u+at

v^2 = u^2 + 2as

S = ut+ (1/2) at^2

For this question, we will be using the first one.

Third Step: Solve

V = 0 (the final velocity is 0, because the train stopped)

U = 60 (the train was going at 60 mps)

T = 85 seconds( 1 min and 25 sec)

0 = 60+ 85a

Answer 2

First convert the minutes to seconds. That’s the standard unit for time in physics. 2 minutes is 120 seconds, add that to the 25 second to get 145 seconds.

Use the first kinematic equation Vf = Vi + at. We are given everything here besides acceleration. We know Vf equals zero because it says the train comes to a stop.
0 = 60m/s + a*145s
-60m/s = 145a
a = -60/145 = -12/29 m/s^2