Dynamics Help (1 Viewer)

[nimrod_dookie]

Hi everyone,

This is probably the most basic question to ask but I haven't done any rectilinear motion in 2 years and I'm so rusty, especially since all the theory and examples presented so far are in the context of DE's given to us.

The question is :

A train travels between two stations 2.9 km apart. If the maximum acceleration is 2.2 m/s^2 and the greatest deceleration is 3.3 m/s^2, find the shortest time between the stations if the maximum speed allowed is 108 km/hr.

Any help would be greatly appreciated. I feel so dumb right now...brain still stuck in statics mode from last sem.

Cheers

 

[Affinity]

convert everything to k-m-s.
so they are 2900 m apart, and max speed is 30m/s

It takes 30/2.2 seconds to get it to the max speed, during this time a distance of 15*30/2.2 metres is travelled (average speed = 15)

to decelerate from 30m/s to 0 it takes 30/3.3 seconds, during which the distance travelled is 15*30/3.3

that leaves (2900 - 15*30/2.2 - 15*30/3.3) metres in the middle, where the train travels at 30 m/s

so total time =
(2900 - 15*30/2.2 - 15*30/3.3) /30 + 30/2.2 + 30/3.3 = 108.030303 seconds

 

[nimrod_dookie]

Thankyou Affinity .