Projectile motion - equations giving different answers?

[lilyxmo]

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.

 

[rcgldr]

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.

 

[lilyxmo]

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

 

[rcgldr]

Assuming 60 degrees is from horizontal as you've shown, it looks OK so far.

 

[Nickie]

There could be a few reasons why the two methods are giving different answers. First, make sure that you are using the correct values for the initial velocity and angle. Double check your calculations to ensure that you are using the correct components for vx and vy.

Another possible reason for the discrepancy could be due to rounding errors or significant figures. Make sure that you are using enough significant figures in your calculations to minimize any errors.

Lastly, it is possible that one of the equations you are using is not appropriate for this specific problem. It is always important to carefully choose the equations you use and make sure they are applicable to the problem at hand.

To determine which answer is correct, you could try using a different method to solve the problem, such as using the kinematic equations or graphing the motion. This way, you can compare your answers and see which one is most accurate.

In terms of the negative distance, it is important to consider the direction of the motion when using the equations. In this case, the object is being launched downwards, so the distance should be negative. However, this does not necessarily mean that your answer is incorrect. As long as you are consistent with your direction and use the correct sign conventions, your answer should be accurate.

In summary, it is important to double check your calculations and consider the appropriateness of the equations being used. If you are still unsure, try using a different method to solve the problem and compare your answers.