Shooting Rifles from Platforms - Projectile question

• Niner1309
In summary, a student attempted to find the time it takes for a bullet to hit the ground based on the initial vertical velocity and the horizontal distance. The equation they used was t=\sqrt{\frac{2d}{a}}. However, they were not using the bullet speeds they were given, and the results were different if the rifles were at an angle.
Niner1309

Homework Statement

Hi all! What a great site, thanks in advance for any help! My question is written:
The six figures below show rifles that are being fired horizontally, i.e. straight out, off platforms. The bullets fired from the rifles are all identical, but the rifles propel the bullets at different speeds. The specific speed of each bullet and the height of the platform are given. All of the bullets miss the targets and hit the ground.

Rank these bullets, from longest to shortest, on the basis of how long it takes a bullet to hit the ground. That is, put first the bullet that will take the longest time from being fired to hitting the ground, and put last the bullet that will take the shortest time.

Following this are six pictures of identical trees, each with a platform and a little man with a rifle. There are distance measurements beside the trees for the height of each platform, and speeds above each rifle.

The first tree has a platform height of 20 m, and a bullet speed of 1200 m/s.
The second tree has a platform height of 40 m, and a bullet speed of 500 m/s.
The third tree has a platform height of 40 m, and a bullet speed of 800 m/s.
And so on.

Homework Equations

My instinct is to use the equation:
$t=\sqrt{\frac{2d}{a}}$

I know the distance and the acceleration (-9.8 m/s^2), so i get an answer, the problem is if I use this equation to get the time, I'm not using the bullet speeds I'm given. Is that correct?

The Attempt at a Solution

$t= \sqrt{\frac{2(-20 m)}{-9.8 m/s^2}}$
t=2.0s

Is this right? Thanks again for your help!

The Attempt at a Solution

Niner1309 said:
My instinct is to use the equation:
$t=\sqrt{\frac{2d}{a}}$

You can use this equation to relate time and vertical displacement if the initial vertical velocity is zero. Is it?

Yes, I think is. The horizontal velocity is the speed of the bullet fired from the rifle. That makes the vertical velocity zero. (I think.)

Then you should not be surprised that speed does not affect your results.

Would anything change if the rifles were at an angle with the horizontal?

Yes, then I would have to use the velocity for the calculation, not the distance. Hmmm, good point!

You would have to use both. Anyway, I think you know how to solve this problem as stated.

1 person
Thank you so much, you're right, I think I do know what to do now!

1. What is the purpose of shooting rifles from platforms?

The purpose of shooting rifles from platforms is to provide a stable and elevated position for the shooter to aim and fire their rifle from. This can improve accuracy and precision, particularly for long-range shots.

2. What types of platforms are commonly used for shooting rifles?

There are several types of platforms that are commonly used for shooting rifles, including shooting benches, bipods, shooting sticks, and tree stands. Each type of platform has its own advantages and is suited for different shooting situations.

3. How does shooting from a platform affect the trajectory of the projectile?

Shooting from a platform can affect the trajectory of the projectile in several ways. The stability of the platform can reduce recoil and improve accuracy, while the elevation can affect the angle and distance of the shot. It is important for shooters to practice and adjust their aim accordingly when shooting from a platform.

4. Are there any safety concerns when shooting rifles from platforms?

Yes, there are safety concerns when shooting rifles from platforms. It is important to ensure that the platform is stable and secure to prevent accidents or injuries. It is also essential to follow all safety protocols, such as wearing ear and eye protection and properly storing and handling firearms.

5. Are there any regulations or restrictions when shooting rifles from platforms?

Regulations and restrictions for shooting rifles from platforms may vary depending on the location and type of platform. It is important to research and follow all local laws and regulations, as well as any guidelines set by the platform manufacturer. Additionally, it is crucial to always practice safe and responsible shooting practices when using a platform.

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