The problem involves a boy throwing a ball vertically from the top of a building, with various questions regarding the ball's motion, including its initial velocity, maximum height, velocity at different points, and time of flight. The subject area is kinematics, focusing on motion under constant acceleration due to gravity.
The discussion is ongoing, with participants providing guidance on using kinematic equations and exploring different interpretations of the problem. There is a collaborative effort to clarify concepts and address misunderstandings, but no consensus has been reached on all aspects of the problem.
Participants note potential constraints in the problem, such as the assumption of constant acceleration and the effects of gravity, as well as the lack of explicit information regarding the ball's initial velocity and displacement. Some express uncertainty about the realism of the scenario, particularly regarding the height the ball could reach.
Looks good! (For the last two, you know that the acceleration is 9.8 m/s^2 downward. So you may want a minus sign.)lNVlNClBLE said:d)
-40 = 39.2t + (1/2)(-9.8)(t)^2
-40 = 39.2t + (-4.9)(t)^2
-4.9t^2 + 39.2t + 40 = 0
4.9t^2 - 39.2t - 40 = 0
= 39.2 plus/minus sqrt (1536.64 + 784)/9.8
= 39.2 plus/minus sqrt (2320.64)/9.8
= 39.2 plus/minus 48.17/9.8
t = 8.92 seconds
WHEW.
e) v = Vo + at
v = 39.2 + (-9.8)(8.92)
v = 39.2 + (-87.42)
v = -48.22
v = 48.22 m/s
f) 9.8 m/s^2
g) 9.8 m/s^2?
Looks good. Yes, the negative time solution is not relevant for this problem.lNVlNClBLE said:Phew. Long time since I used the quadratic. Can you check to see if that's right?
Also, I've never used it before in physics, so I'm assuming the whole negative part of the plus/minus can be ignored since there's no such thing as negative time.
Using an "up = positive" convention, you'd need a minus sign.EDIT: Completed the rest of the problem with that time. I assume f is also just 9.8 m/s^2. If so, are those accelerations -9.8, or just 9.8?
Doc Al said:Looks good. Yes, the negative time solution is not relevant for this problem.
Using an "up = positive" convention, you'd need a minus sign.
As SHISHKABOB says, you'll use the same formulas and methods. Just apply them to the vertical motion separately. Start by figuring out the y-component of the initial velocity.lNVlNClBLE said:One more question. I started another problem of parabolic motion, and I only got stuck at one part. I need to find the total height of a ball thrown off the top of a building, when the height of the building is 45m, and the ball is thrown at 20m/s at a 30 degree angle.
What formula would I derive the Ymax from? I already solved the x distance displacement and the final velocity.