Simple Projectile Motion Help: Finding the Height of a Table

[jillime]

Hey guys, I'm not great at physics and my brain sometimes just doesn't get the sort of "implied" aspects of a problem. So I could use some help with an easy question.

In projectile motion, there are certain constants given particular circumstances, right?

I have to find the height of a table given the speed of a ball rolling off of it, and the distance away from the table that it lands.

But I don't know how to fill in the holes. For example, I keep wondering about velocity in the Y direction. I don't know if its 9.8, or if that's the acceleration, and I just confuse myself with my lack of confidence about what's what, what's constant, zero, etc.

having not given you guys any mathematical insight into this problem, could someone just relay to me what you would already know, given this particular circumstance?

 

[dimension10]

Hey guys, I'm not great at physics and my brain sometimes just doesn't get the sort of "implied" aspects of a problem. So I could use some help with an easy question.

In projectile motion, there are certain constants given particular circumstances, right?

I have to find the height of a table given the speed of a ball rolling off of it, and the distance away from the table that it lands.

But I don't know how to fill in the holes. For example, I keep wondering about velocity in the Y direction. I don't know if its 9.8, or if that's the acceleration, and I just confuse myself with my lack of confidence about what's what, what's constant, zero, etc.

having not given you guys any mathematical insight into this problem, could someone just relay to me what you would already know, given this particular circumstance?

For the first part, try using s=1/2 gt^2. You can calculate t using the initial velocity and the final velocity. I'm assuming the initial and final velocities are given. So, for example, if the initial velocity is 0 and the final velocity is 9.80665m/s^2, then the time is 1s. Then s=g/2, the numbers, that is. Around 4.9033m, if you consider the significant figures.

For the second part, try to break the velocity vector down into 2 components. The y-component would be v_0+gt. Where g is acceleration due to gravity ~9.8066m/s^2. The velocity is certainly not 9.8, its the acceleration. The velocity is not constant as gravity is acting on the ball.

Sorry for not using $\LaTeX$

 

[Villyer]

How I approach this is taking what you know and asking myself "What can I find out with this?".

You know the initial horizontal velocity, and horizontal displacement. By realizing that the horizontal acceleration is 0, you can find the time.
Now, in the vertical direction, you know time (since time is the same for each direction in projectile motion). You also know that the ball is rolling off of a table, so its initial velocity in the y direction is 0. You also know that the acceleration in the y direction is g. So using those three known quantities, you can find the vertical displacement.


I guess that the four bold statements are then the implied givens for this problem.

 

[azizlwl]

This a 2 dimension problem.

Normally we encountered 1 dimension case if a car is moving along a straight line. It will be a distance from the origin by multiplying velocity with time. If it is accelerating we use SUVAT equation.

In the 2 dimension, x or y are lines.
In 3D, x, y and z are planes.

Now back 2D, displacement x is a vertical line from +∞ to -∞ intersect x-axis at x unit from origin. Likewise the y line.

Both lines are moving according its function, for x=vt
and for y=ut+1/2at²
.

Thus we are only interested in the intersection on both lines, since there is only one object.
The intersection is the point where the object lies

 

[asteriatic]

Hi there,

First of all, don't worry about not being great at physics. It can be a complex subject, but with some practice and understanding of the basic principles, you can definitely improve.

In projectile motion, there are a few key concepts that you need to understand. The first one is that the motion of a projectile can be broken down into two components: horizontal and vertical. In your problem, the ball is rolling off a table, so we can assume that its initial velocity in the horizontal direction is constant (since it is not being acted upon by any external forces). This means that we can use the formula v = d/t to find the initial horizontal velocity, where v is the velocity, d is the distance the ball travels, and t is the time it takes to travel that distance.

The second concept is that in the absence of air resistance, the acceleration due to gravity in the vertical direction is constant and equal to 9.8 m/s². This means that the ball will accelerate downward at a rate of 9.8 m/s² as it falls off the table.

Now, to find the height of the table, we can use the formula h = (v²sin²θ)/(2g), where h is the height of the table, v is the initial velocity in the vertical direction, θ is the angle at which the ball is launched (in this case, it is rolling off the table, so θ = 90°), and g is the acceleration due to gravity. Since we know the initial horizontal velocity (found using v = d/t) and the distance the ball travels before hitting the ground, we can find the initial vertical velocity using the formula v = d/t.

To summarize, in order to find the height of the table, you will need to use the following information: the distance the ball travels before hitting the ground, the initial horizontal velocity (found using v = d/t), and the acceleration due to gravity (which is 9.8 m/s²). I hope this helps and good luck with your problem!