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Yapper
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For phys 170 we do assignments on a website from the textbook edugen.wiley.com.
A red train traveling at 72 km/h and a green train traveling at 144 km/h are headed toward each other along a straight, level track. When they are 870 m apart, each engineer sees the other's train and applies the brakes. The brakes slow each train at the rate of 1.0 m/s^2. Is there a collision?
If so, give (a) the speed of the red train, (b) the speed of the green train, and (c) the separation between the trains when they collide (0 m).
If not, give (a) the speed of the red train (0 m/s), (b) the speed of the green train (0 m/s), and (c) the separation between the trains when they stop.
v0= initial velocity
v=v0+at
dx=(1/2)at^2 + v0t
72km/h = 20 m/s 144 km/h = 40 m/s
Ok so I checked the stopping distances and the red train will stop after 20 seconds, 200 m farther down and after that 20 sec the green train will be (1/2)(-1)20^2 + 40(20) = 600m farther down the track, so I assumed the red train's velocity to be 0m/s since it stops before the collision.
Then for the green train I set 1/2(-1)x^2 +40x = 670, to see how long it would take for the green train to hit the stationary red train, and solved for x. I got 23.8755 seconds. Then solved for velocity 40-23.8755 =16.1245 m/s.
So I inputed a) 0 m/s b) 16.1245 m/s c) 0 m
The website said I was wrong and after many different tries it told me that the answer was:
(a)
Number: 3.127717305696
Units: m/s
(b)
Number: 23.127717305696
Units: m/s
(c)
Number: 0
Units: m
Please help, What did I do wrong? or is the website wrong
Homework Statement
A red train traveling at 72 km/h and a green train traveling at 144 km/h are headed toward each other along a straight, level track. When they are 870 m apart, each engineer sees the other's train and applies the brakes. The brakes slow each train at the rate of 1.0 m/s^2. Is there a collision?
If so, give (a) the speed of the red train, (b) the speed of the green train, and (c) the separation between the trains when they collide (0 m).
If not, give (a) the speed of the red train (0 m/s), (b) the speed of the green train (0 m/s), and (c) the separation between the trains when they stop.
Homework Equations
v0= initial velocity
v=v0+at
dx=(1/2)at^2 + v0t
The Attempt at a Solution
72km/h = 20 m/s 144 km/h = 40 m/s
Ok so I checked the stopping distances and the red train will stop after 20 seconds, 200 m farther down and after that 20 sec the green train will be (1/2)(-1)20^2 + 40(20) = 600m farther down the track, so I assumed the red train's velocity to be 0m/s since it stops before the collision.
Then for the green train I set 1/2(-1)x^2 +40x = 670, to see how long it would take for the green train to hit the stationary red train, and solved for x. I got 23.8755 seconds. Then solved for velocity 40-23.8755 =16.1245 m/s.
So I inputed a) 0 m/s b) 16.1245 m/s c) 0 m
The website said I was wrong and after many different tries it told me that the answer was:
(a)
Number: 3.127717305696
Units: m/s
(b)
Number: 23.127717305696
Units: m/s
(c)
Number: 0
Units: m
Please help, What did I do wrong? or is the website wrong