Two trains heading straight for each other on the same track are 250 m apart when their engineers see each other and hit the brakes. The A, heading west at 96 km/h, slows down, accelerating at an average of -4 m/s^2, while the B, traveling at 110 km/h, slows down, accelerating at an average of -3 m/s^2. Will they collide?(adsbygoogle = window.adsbygoogle || []).push({});

I solved it this way :

a_T = The resultant of two accelerations = -7

V_A = 96 km/h

V_B = 110 km/h

V_T = V_B + V_A = 206 km/h = 57.22 m/s

And considered (V_T)_final = 0.

Plugging into this formula : S = - [(V_T)^2 ] / 2 a_T; S = 233.9. So two trains won't collide.

My answer for S is not the same as the one in the solutions manual, 244.5 m. Why is my answer 233.9 ?

The book has solved that problem in a different way, and I can do it so, but I'm interested to know why my answer is wrong.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Will they collide? No but

**Physics Forums | Science Articles, Homework Help, Discussion**