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

Projectile motion - equations giving different answers?

  • Thread starter lilyxmo
  • Start date
  • #1
5
0

Homework Statement



If an object is being launched from the top of a staircase 1.31m high from a pipe 16cm long, at an angle of 60 degrees. Find where the object will land if the initial velocity is 5.442m/s.

Homework Equations


dx = 2v1^2sinθcosθ / g

dy = vyΔt+1/2gΔt^2

dx = vxΔt


The Attempt at a Solution


I found the components to be
vx = 2.721
vy = 4.713

then i just used these in the two methods
the answers should both be the same, but the dx i got from both was very different
Am i doing something wrong? which one would be the correct answer?



Also, for the first method, i put 120 degrees as negative as it is below my reference point, or it would give me a neg. distance.
 

Attachments

Answers and Replies

  • #2
rcgldr
Homework Helper
8,682
520
There is an issue with the wording of the problem. Is the 1.3 m the exit point of the pipe or the base of the pipe? If it's the base, then you'd need to take into account the pipe's 16 cm length. If it's the exit point you wouldn't need to know the length of the pipe, so it seems more likely that 1.3 m is the base of the pipe.
 
  • #3
5
0
to the base of the pipe
so the total height would be the stairs + height of top of stairs to the opening of the pipe

which is 1.324m
 

Attachments

  • #4
rcgldr
Homework Helper
8,682
520
Assuming 60 degrees is from horizontal as you've shown, it looks OK so far.
 

Related Threads on Projectile motion - equations giving different answers?

Replies
2
Views
1K
  • Last Post
Replies
1
Views
2K
Replies
12
Views
2K
Replies
4
Views
3K
Replies
2
Views
1K
Replies
1
Views
6K
Replies
2
Views
1K
Replies
15
Views
2K
Replies
4
Views
2K
Replies
3
Views
3K
Top