Help with projectile motion problem

In summary, The problem involves projectile motion of a ball kicked horizontally with an initial speed of 9.0 m/s and a constant horizontal acceleration of 12 m/s^2 due to a blowing wind. The goal is to determine the height of the boardwalk above water and where the ball will fall if the wind reverses direction while maintaining the same strength. The information provided includes the horizontal and vertical accelerations, as well as the initial speed of the ball. The conversation includes a discussion of the confusion surrounding the question and the realization that the ball still falls vertically while being blown back horizontally by the wind. The solution requires considering the horizontal and vertical components separately.
  • #1
brightside
2
0
I'm having some difficulty with a problem about projectile motion. Just some background about me: I'm just beginning an intro to physics course and I don't have much of a math/science background, so I apologize if I make any errors regarding equations and such.

The problem:

A boy kicks a ball horizontally near the edge of a boardwalk, with an initial speed of 9.0 m/s. A blowing wind gives the ball a constant horizontal acceleration of 12 m/s^2. The ball falls into the water directly under the boy. Ignore the effect of air resistance on the vertical motion of the ball.

A) Determine the height of the boardwalk above water.
B) If the blowing wind reverses direction while maintaining the same strength, where does the ball fall when it is kicked with the same initial speed?

I don't have much byway of an attempted solution for A (I haven't even looked at B yet) because I'm really not even sure where to start, but this is the information I know I have:

ax = 12m/s^2
ay = g = -9.8m/s^2
v0 = 9m/s

I tried to plug it into y = y0 + vy0t + 1/2ayt^2 to firstly find t, but I don't have vy0. In the other questions I've been doing, I've been given the angle in relation to the x axis, which allows me to find vy0 and vx0 using v0cosθ and v0sinθ, respectively. But I don't see how to find it with just the information I have.

So I'm left feeling rather lost regarding this question. Can anyone point me in the right direction?
 
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  • #2
You don't have enough information. Are you sure you have fully stated the problem as it was written?
 
  • #3
phinds said:
You don't have enough information. Are you sure you have fully stated the problem as it was written?

There's enough information :smile: It's just provided in a sneaky fashion. Consider where the ball lands in the horizontal direction...
 
  • #4
phinds said:
You don't have enough information. Are you sure you have fully stated the problem as it was written?

Yes, that's the question word for word.


gneill said:
There's enough information :smile: It's just provided in a sneaky fashion. Consider where the ball lands in the horizontal direction...

"The ball falls into the water directly under the boy" - that's just confusing me further :) If it lands directly below him, it would seem like there was no projection. But since there is projection, does that mean the wind is blowing towards him and sends the ball back where it started?
 
  • #5
brightside said:
"The ball falls into the water directly under the boy" - that's just confusing me further :) If it lands directly below him, it would seem like there was no projection. But since there is projection, does that mean the wind is blowing towards him and sends the ball back where it started?

Yes, that's it, at least for the horizontal direction. The ball still falls vertically as usual.
 
  • #6
gneill said:
There's enough information :smile: It's just provided in a sneaky fashion. Consider where the ball lands in the horizontal direction...

You're right, of course. That slid right by me. Good catch.
 
  • #7
gneill said:
Yes, that's it, at least for the horizontal direction. The ball still falls vertically as usual.

I am sure you mean the ball accelerates vertically in the usual way. The ball actually travels on a curved path (vertically) that happens to end up directly below the boy.
 
  • #8
PeterO said:
I am sure you mean the ball accelerates vertically in the usual way. The ball actually travels on a curved path (vertically) that happens to end up directly below the boy.
Certainly. I was referring to the horizontal and vertical components separately. Sorry if that wasn't clear.
 

FAQ: Help with projectile motion problem

1. What is projectile motion?

Projectile motion is the motion of an object through the air when it is given an initial velocity and then allowed to move freely under the influence of gravity.

2. How do I solve a projectile motion problem?

To solve a projectile motion problem, you need to break it down into two components: horizontal and vertical. Use the equations of motion to find the object's position, velocity, and acceleration in both components at different time intervals.

3. How do I find the initial velocity in a projectile motion problem?

The initial velocity can be found by analyzing the given information in the problem. If the object was launched from a height, you can use the equation v = √(2gh) to find the initial velocity, where g is the acceleration due to gravity and h is the initial height.

4. What is the importance of angle in projectile motion?

The angle at which an object is launched affects its trajectory and range. A higher angle will result in a longer flight time and distance, while a lower angle will result in a shorter flight time and distance. The optimal angle for maximum range is 45 degrees.

5. How does air resistance affect projectile motion?

Air resistance, also known as drag, can affect the motion of a projectile by slowing it down. As the object moves through the air, it experiences a force in the opposite direction of its velocity, reducing its speed. This can affect the object's trajectory and distance traveled.

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