Can someone explain this physics problem to me?

Question

You are on a train that is traveling at 3.0 m/s along a level straight track. Very near and parallel to the track is a wall that slopes upward at a 12° angle with the horizontal. As you face the window (0.96 m high, 2.2 m wide) in your compartment, the train is moving to the left, as the drawing indicates. The top edge of the wall first appears at window corner A and eventually disappears at window corner B. How much time passes between appearance and disappearance of the upper edge of the wall?

http://www.webassign.net/CJ/02_12.gif (image for problem)

can some explain how to do it please because i'm utterly confused

Answer 1

Well, we first use a bit of trigonometry to find how far horizontally you have traveled if you needed to see the 12° wall rise above you. Check out the picture at:

http://student.physics.ucdavis.edu/~mwoo...

We have the horizontal distance (x in the picture) as being 4.52 m, but that does not include a little bit more the window goes so that the wall goes from the upper left corner of the window to the upper right (point B). So we add the length of the window: 4.52 m + 2.2 m = 6.72 m. We can use the speed that the train is going to figure out how long it takes to travel that horizontal distance.

time = (distance) / (speed) = (6.72 m) / (3.0 m/s) = 2.24 seconds