Question on motion in two dimensions:

AI Thread Summary
The discussion revolves around solving a projectile motion problem involving a baseball hit at a 42° angle, clearing a height of 23.6 m at a horizontal distance of 130 m. The user is struggling to determine the initial speed, time of flight, and velocity of the ball at the peak of its trajectory. They have attempted to use trigonometry and kinematic equations but are encountering difficulties in eliminating variables to find the initial velocity. Despite calculating values for horizontal and vertical components, they received incorrect feedback from their assignment platform, indicating potential rounding errors or miscalculations. The conversation emphasizes the importance of precise calculations and understanding the relationships between the projectile's motion components.
integra2k20
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OK, I've been trying to get problems like these where you are given the angle (but not the velocity) of the direction in which a projectile is fired. I have tried as many ways as i could conceive using kinematics, but i keep getting stuck. If anyone could just give me an idea how to go about getting a little more info so i can complete the problem, it would be greatly appreciated.

Barry Bonds hits a home run so that the baseball just clears the top row of bleachers, 23.6 m high, located 130 m from the home plate. The ball is hit at an angle of 42° to the horizontal, and air resistance is negligible. Assume that the ball is hit at a height of 1.00 m above the ground. Find the following values.
(a) the initial speed of the ball
(m/s)

(b) the time at which the ball reaches the cheap seats
(s)

(c) the velocity of the ball when it passes over the top row
(____i+____j m/s)

(d)the speed of the ball when it passes over the top row
(m/s)
 
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I think a good first step would be to use some trig to figure out the vertical distance the ball travels
 
After drawing a diagram, write down the equations of displacement of the ball for the x and y direction separately. What do you know about the initial position of the ball? What do you know about the final position of the ball? Eliminate the variable t from one of the equations, to get the initial velocity. The rest should be easy.
 
valueduser said:
I think a good first step would be to use some trig to figure out the vertical distance the ball travels

how would you do this, since the path would be parabolic?

EDIT: the total displacement is 131.9498, still don't get how I am gunna figure it out tho, i drew everything out but can't seem to get it still...
 
Last edited:
i tried what radou said, and it (seemed) to work. i got the values for Vxi and Vyi, then found Vi from that. it all worked out the way it should have an di checked my answer. these are the values i got:

Vxi = 174.9323 m/s
Vyi = 33.7752 m/s
Vi = 235.3946 m/s

t = .7431 seconds

with these values, i was able to calculate that the ball was at the following points at t= .7431: x = 129.9922 (which is right, its supposed to be 130, just some round off error). y = 23.3926 (should be 23.6, again, roundoff error). Since those values are so close, webassign should have no problem accepting those answers, but it says theyre wrong...
 

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