# Projectile - Speed and angle for football just clearing goalposts

• ken.drea
In summary, to find the initial speed and angle of a football kicked from 35 yards that barely clears a 10-foot goal post and lands 8 feet behind it, we can use the equations for x(t) and y(t) and eliminate time to solve for the initial velocity. With three known points on the ball's trajectory and two suvat equations, we can solve for the initial speed and angle of the kick.
ken.drea
Question: A kicker on a football team attempts to kick a field goal from 35 yards. The attempt just clears the goal post that is 10 feet high. The football lands 8 feet behind the plane of the goal. What speed and angle was the football initially kicked? (Use acceleration of gravity as 32 ft/s^2).

Variables given&needed
a= 32ft/s^2
Vi = ?
X= 113 ft (35yrds = 105 ft, then +8ft)
Vyf= 0

At first, I tried plugging them into this equation: Vyf^2 = Vyi^2 + 2ay
I used 10 feet as the y value. I got 25.298 as my Vyi. Then, I solved for the angle by using sine. I got an error. Then I realized that 10 feet is not the full y value, It's only the height of the goal thing.
Now I'm stuck. I was going to find time, but I'm missing a lot of variables. I was going to use it into the formula "x=Vt" to find the velocity.

Note:
a = acceleration
Vi = velocity initial
Vf = velocity final
X = horizontal distance
Y = vertical distance
t =time

Welcome to PF;
You have not used everything you know yet...
You know three points on the ball's trajectory, and you have two suvat equations for the two components of the ball's motion wrt time.

HInt: Try using the equation for x(t) to eliminate t from the equation for y(t)...

Last edited:

## 1. What is the optimal speed for a football to just clear the goalposts?

The optimal speed for a football to just clear the goalposts will vary depending on factors such as the angle and distance from the goalposts. Generally, a speed of around 50-60 miles per hour is considered ideal for a successful goal.

## 2. How does the angle of the ball affect its speed and trajectory when trying to clear the goalposts?

The angle of the ball can greatly affect its speed and trajectory when trying to clear the goalposts. A lower angle will result in a faster speed, while a higher angle will result in a slower speed but a higher arc. Adjusting the angle can also alter the direction of the ball.

## 3. Is there a specific technique for kicking a football to just clear the goalposts?

Yes, there are various techniques for kicking a football to just clear the goalposts. One common technique is the "knuckleball" technique, where the player strikes the center of the ball with the laces of their foot, causing the ball to have minimal spin and a unpredictable flight path.

## 4. How does air resistance affect the speed and trajectory of a football when trying to clear the goalposts?

Air resistance can greatly affect the speed and trajectory of a football when trying to clear the goalposts. The more air resistance, the slower the ball's speed will be and the more it will curve. This is why players will often adjust their kick based on wind conditions.

## 5. What other factors besides speed and angle can impact a football's ability to clear the goalposts?

Other factors that can impact a football's ability to clear the goalposts include the weight and shape of the ball, the player's technique and strength, and external factors like wind and weather conditions. The condition of the field, such as the type of turf or any divots, can also affect the ball's trajectory.

• Introductory Physics Homework Help
Replies
16
Views
2K
• Introductory Physics Homework Help
Replies
5
Views
365
• Introductory Physics Homework Help
Replies
3
Views
1K
• Introductory Physics Homework Help
Replies
23
Views
2K
• Introductory Physics Homework Help
Replies
7
Views
1K
• Introductory Physics Homework Help
Replies
2
Views
3K
• Introductory Physics Homework Help
Replies
3
Views
510
• Introductory Physics Homework Help
Replies
53
Views
4K
• Introductory Physics Homework Help
Replies
2
Views
1K
• Introductory Physics Homework Help
Replies
18
Views
310