A train 300 m long is moving on a straight track with a speed of 83.5 km/h. The engineer applies the brakes at a crossing, and later the last car passes the crossing with a speed of 15.6 km/h. Assuming constant acceleration, determine how long the train blocked the crossing. Disregard the width of the crossing.
I would really appreciate some input on the problem :)
2006-09-06 11:16:16 · 4 answers · asked by Anonymous in Education & Reference ➔ Homework Help
a is acceleration (a constant), v is velocity, t is time, d is distance (300 m = 0.3 km), vo is initial velocity.
Eq 1: v = at + vo
Eq 2: d = 1/2 at^2 + vo t
Eq 1: 15.6 = at + 83.5
Eq 3: at = 15.6 - 83.5 = -67.9
Eq 3: a = -67.9/t
Eq 2: 0.3 = 1/2(-67.9/t) t^2 + 83.5 t
0.3 = -33.95 t + 83.5 t = 49.55 t
t = 0.3/49.55 = 0.00605 hrs. x 3600 sec/hr
t = 21.8 seconds
This rounds off to 22 seconds. (Answer)
2006-09-06 11:42:56 · answer #1 · answered by bpiguy 7 · 0⤊ 0⤋
the width of the crossing is the final data you need to find the answer. without that, you could assume the witdh of te crossing was 200 m or 3 m, which would change drastically, i think the only way to answer that question would be to provide an equation, where x equals the length of the crossing. other than that, i don't think it's possible
2006-09-06 18:21:53 · answer #2 · answered by Mickey Blue Eyes 3 · 0⤊ 0⤋
d=((Vi + Vf)/2)*t
d= 300m = 0.3km
Vi= 83.5 km/h
Vf= 15.6km/h
t= ?
.3=((83.5+15.6)/2)*t
.3=49.55t
t=.3/49.55
t= .0061 h
t= 21.96 seconds
2006-09-06 18:31:17 · answer #3 · answered by Steve 1 · 0⤊ 0⤋
f
2006-09-06 18:34:14 · answer #4 · answered by Austin Semiconductor 5 · 0⤊ 0⤋