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An airplane is dropping bales of hay to cattle stranded in a blizzard on the Great Plains. The pilot releases the bales at \(150 \mathrm{~m}\) above the level ground when the plane is flying at \(75 \mathrm{~m} / \mathrm{s}\) in a direction \(55^{\circ}\) above the horizontal. How far in front of the cattle should the pilot release the hay so that the bales land at the point where the cattle are stranded?

Short Answer

Expert verified
The pilot should release the hay when the plane is approximately \[x = v_{x0}*t\] meters in front of the cattle.

Step by step solution

01

Determine the components of the initial velocity

Initial velocity can be broken down into horizontal and vertical components using the direction angle. The horizontal component of velocity is given by \(v_{x0} = v_{0} cos(\Theta)\) where \(v_{0}\) is the magnitude of the initial velocity and \(\Theta\) is the angle it makes with the horizontal. And similarly, the vertical component is given by \(v_{y0} = v_{0} sin(\Theta)\). So, \(v_{x0} = 75 cos(55)\) and \(v_{y0} = 75 sin(55)\)
02

Time of Flight

The next step is to calculate the time it takes for the bale to hit the ground. This is determined using the equation of motion \(y = v_{y0}t - (1/2)gt^2\), where \(y\) is the vertical displacement (150m), \(g\) is the acceleration due to gravity (9.8 m/s^2) and \(t\) is the time we are trying to find. Rearranging for \(t\), we can find the roots of the resulting quadratic equation is \(at^2 + bt + c = 0\) where \(a = -1/2g\), \(b= v_{y0}\) and \(c= -y\). The roots of this equation will give us two possible times (upward and downward parts of the trajectory), and we choose the larger of the two as the time when the projectile hits the ground.
03

Calculate horizontal distance

Finally, the horizontal distance can be determined using the time of flight and the horizontal component of the initial velocity. The formula used is \(x = v_{x0}*t\) which provides the answer to the problem we are solving.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding Initial Velocity Components
To fully comprehend projectile motion, we first need to break down the initial velocity into its horizontal and vertical components. For an object moving through the air, these two components are governed by different forces and thus behave independently.

In the case of the bales of hay, the pilot must release them with a certain speed at a specific angle to ensure they land at the desired location. Here, the angle provided is 55 degrees above the horizontal, and the initial speed is 75 m/s. Using trigonometry, we can calculate the components.

The horizontal component \(v_{x0}\) deals with the distance covered and isn't affected by gravity. It can be found using the cosine function: \(v_{x0} = v_{0} \cdot \cos(\Theta)\). Conversely, the vertical component \(v_{y0}\) which dictates the time airborne, is influenced by gravity and is calculated with the sine function: \(v_{y0} = v_{0} \cdot \sin(\Theta)\). Understanding these components is crucial for mapping the projectile's path.
Time of Flight Calculation
Onward to the time of flight calculation, which pinpoints how long the bales are airborne before reaching the ground. This time period is essential for determining where the bales will land relative to the release point. We solve for the time using the vertical motion equation.

Given the initial vertical velocity \(v_{y0}\) and the height from which the bales are released, we can set up the equation \[y = v_{y0}t - \frac{1}{2}gt^2\], where \(-y\) represents the vertical distance to the ground (150 m in this case) and \(g\) is the familiar acceleration due to gravity, typically 9.8 m/s^2. By rearranging this into a standard quadratic form, we can then apply methods for solving quadratic equations to find the time of flight \(t\). It's important to select the positive root as it corresponds to the actual time the bales will take to hit the ground.
Applying the Projectile Range Formula
Having calculated the horizontal velocity and time of flight, we are now poised to use the projectile range formula to find the horizontal distance, and thus, how far in front of the stranded cattle the pilot should release the hay bales.

The formula we use is simply \(x = v_{x0} \cdot t\), where \(x\) is the range, \(v_{x0}\) is the horizontal component of initial velocity, and \(t\) is the time of flight we've calculated. By plugging in these values, we can determine how far the bales travel horizontally before touching down. This formula assumes we are neglecting air resistance and any other forces aside from gravity.

Understanding that horizontal motion is constant and not affected by gravity (in our ideal projectile motion scenario) while the vertical motion is uniformly accelerated due to gravity is key to successfully solving these kinds of problems.

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Most popular questions from this chapter

A man stands on the roof of a 15.0 -m-tall building and throws a rock with a speed of \(30.0 \mathrm{~m} / \mathrm{s}\) at an angle of \(33.0^{\circ}\) above the horizontal. Ignore air resistance. Calculate (a) the maximum height above the roof that the rock reaches; (b) the speed of the rock just before it strikes the ground; and (c) the horizontal range from the base of the building to the point where the rock strikes the ground. (d) Draw \(x-t, y-t, v_{x}-t,\) and \(v_{y}-t\) graphs for the motion.

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The position of a dragonfly that is flying parallel to the ground is given as a function of time by \(\vec{r}=[2.90 \mathrm{~m}+\) \(\left.\left(0.0900 \mathrm{~m} / \mathrm{s}^{2}\right) t^{2}\right] \hat{\imath}-\left(0.0150 \mathrm{~m} / \mathrm{s}^{3}\right) t^{3} \hat{\jmath} .\) (a) At what value of \(t\) does the velocity vector of the dragonfly make an angle of \(30.0^{\circ}\) clockwise from the \(+x\) -axis? (b) At the calculated in part (a), what are the magnitude and direction of the dragonfly's acceleration vector?

On level ground a shell is fired with an initial velocity of \(40.0 \mathrm{~m} / \mathrm{s}\) at \(60.0^{\circ}\) above the horizontal and feels no appreciable air resistance. (a) Find the horizontal and vertical components of the shell's initial velocity. (b) How long does it take the shell to reach its highest point? (c) Find its maximum height above the ground. (d) How far from its firing point does the shell land? (e) At its highest point, find the horizontal and vertical components of its acceleration and velocity.

A movie stuntwoman drops from a helicopter that is \(30.0 \mathrm{~m}\) above the ground and moving with a constant velocity whose components are \(10.0 \mathrm{~m} / \mathrm{s}\) upward and \(15.0 \mathrm{~m} / \mathrm{s}\) horizontal and toward the south. Ignore air resistance. (a) Where on the ground (relative to the position of the helicopter when she drops) should the stuntwoman have placed foam mats to break her fall? (b) Draw \(x-t, y-t, v_{x}-t,\) and \(v_{y}-t\) graphs of her motion.

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