• Support PF! Buy your school textbooks, materials and every day products Here!

Thrown Ball on Moving Train

  • Thread starter Juntao
  • Start date
  • #1
45
0
A Physics 111 student is riding on a flatcar of a train traveling along a straight horizontal track at a constant speed of 12 m/s. The student throws a ball into the air on a trajectory that she observes to make an initial angle of 53° with respect to the horizontal along the same line as the track. The student's TA, who is standing on an embankment nearby, observes the ball to rise straight up vertically.

How high does the ball rise in meters?

-----------------------
Of course, I tried this equation, (vy)^2=(v0 sin theta)^2-2(g)(y-y0)
where vy is final velocity in y component
v0=initial velocity
g=9.8 m/sec/sec
y0=0

So if the ball reaches top of its height, its velocity is zero, thus
0=(12*sin 53)^2-(2*9.8)(y)
and I get y=4.69 meters.

Okay, this isn't right, and I'm probably going at this problem the wrong way, right? Argh!
 

Answers and Replies

  • #2
HallsofIvy
Science Advisor
Homework Helper
41,833
955
It looks to me like you are assuming vo= 12 m/s and there is no reason to do that. What you are told is that the ball rises vertically relative to the ground. Since the train is moving at 12 m/s, the HORIZONTAL COMPONENT of the ball (relative to the train) must be 12 m/s. Use that to find vo.
(The student is, by the way, throwing the ball opposite to the direction of the train.)
 

Related Threads on Thrown Ball on Moving Train

Replies
19
Views
676
  • Last Post
Replies
11
Views
2K
  • Last Post
Replies
11
Views
4K
  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
6
Views
6K
  • Last Post
Replies
2
Views
6K
  • Last Post
Replies
2
Views
10K
  • Last Post
Replies
1
Views
458
  • Last Post
Replies
5
Views
3K
Top