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A hose lying on the ground shoots a stream of water upward at an angle of \(40^{\circ}\) to the horizontal. The speed of the water is \(20 \mathrm{~m} / \mathrm{s}\) as it leaves the hose. How high up will it strike a wall that is a horizontal distance of \(8.0 \mathrm{~m}\) away?

Short Answer

Expert verified
The water will strike the wall approximately 2.99 meters high.

Step by step solution

01

Identify the Problem

We have a projectile motion problem. The water is being shot at an angle, and we need to find how high up it strikes a wall a given distance away.
02

Break Down Initial Velocity

The initial velocity is given as \( 20 \; m/s \). Break it down into horizontal and vertical components using the angle of projection \( \theta = 40^\circ \).- Horizontal component: \( v_{x} = v \cdot \cos\theta = 20 \cdot \cos(40^\circ) \)- Vertical component: \( v_{y} = v \cdot \sin\theta = 20 \cdot \sin(40^\circ) \).
03

Calculate Time of Flight to Wall

The water travels a horizontal distance of \( 8.0 \; m \). Use horizontal motion, which is at constant velocity, to find the time \( t \) it takes to reach the wall.\[8.0 = v_{x} \cdot t \]Solve for \( t \) using \( v_{x} = 20 \cdot \cos(40^\circ) \).
04

Use Vertical Motion to Find Striking Height

With the time \( t \) calculated, use vertical motion equations to find the height (\( y \)) when the water strikes the wall.The formula for vertical motion is:\[y = v_{y} \cdot t - \frac{1}{2} g t^2\]where \( g = 9.8 \; m/s^2 \). Use \( v_{y} = 20 \cdot \sin(40^\circ) \) to solve for \( y \).
05

Solve for Height

Calculate \( v_{x} \) and \( v_{y} \), then find \( t = \frac{8.0}{v_{x}} \), and finally substitute \( t \) into the vertical motion equation to solve for \( y \). Execute the calculations to find the water strikes the wall at approximately 2.99 meters high.

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Key Concepts

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

Horizontal and Vertical Components
When dealing with projectile motion, it's important to recognize that the initial velocity can be split into two separate directions: horizontal and vertical.
  • **Horizontal Component:** This represents how fast the object moves along the ground. Calculate this using the formula: \( v_{x} = v \cdot \cos(\theta) \). Here \( v \) is the initial velocity, and \( \theta \) is the angle of projection.

  • **Vertical Component:** This shows how fast the object is moving upward. Use the formula: \( v_{y} = v \cdot \sin(\theta) \).
By breaking down the velocity, you can easily track the motion in both directions. This will enable accurate calculations of how far and how high the projectile will travel.
Angle of Projection
The angle of projection is vital in determining the initial path of the projectile. It is the angle at which the object is launched relative to the horizontal.- An angle of 0 degrees means the object is moving entirely horizontally, while an angle of 90 degrees would mean it's moving straight up.
- At angles between these extremes, the projectile will follow a parabolic trajectory.
- This angle affects how the initial velocity is split into the horizontal and vertical components. In our exercise, the water is ejected at an angle of \( 40^{\circ} \). This influences both the speed at which it moves horizontally and how quickly it rises vertically, thus impacting where it will strike the wall.
Constant Velocity
In projectile motion, constant velocity applies to the horizontal movement of the projectile.- **Constant Velocity in Horizontal Motion:** Since there are no forces acting horizontally (ignoring air resistance), the horizontal velocity remains unchanged.
- Use the equation: \( D = v_{x} \cdot t \), where \( D \) is the distance travelled horizontally, \( v_{x} \) is the horizontal component of velocity, and \( t \) is time.This property of motion helps calculate how long it takes for the projectile to reach a specific horizontal distance, such as the wall in our problem. Once you know the time, you can analyze the vertical motion separately.
Vertical Motion Equations
Vertical motion in projectile problems is influenced by gravity, which causes an object in motion to accelerate downward.- **Equation of Vertical Motion:** The key equation to use is \( y = v_{y} \cdot t - \frac{1}{2} g t^2 \).
- Here, \( y \) is the height of the projectile at time \( t \), \( v_{y} \) is the initial vertical velocity, and \( g \) is the acceleration due to gravity (9.8 m/s²).This equation shows how the projectile's height changes over time, considering both the initial rise due to the upward velocity and the downward pull from gravity. By using these calculations, you can determine how high the projectile will be at any given moment, such as when it strikes the wall in the exercise.

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Most popular questions from this chapter

A car is traveling at \(20.0 \mathrm{~m} / \mathrm{s}\) when the driver slams on the brakes and brings it to a straight-line stop in \(4.2 \mathrm{~s}\). What is the magnitude of its average acceleration? The defining scalar equation is \(a_{a v}=\left(v_{f}-v_{i}\right) / t\). Note that the final speed is zero. Here the initial speed is greater than the final speed, so we can expect the acceleration to be negative: $$a_{a v}=\frac{0.0 \mathrm{~m} / \mathrm{s}-20.0 \mathrm{~m} / \mathrm{s}}{4.2 \mathrm{~s}}=-4.76 \mathrm{~m} / \mathrm{s}^{2}$$ Because the time is provided with only two significant figures, the answer is \(-4.8 \mathrm{~m} / \mathrm{s}^{2}\).

A car is accelerating uniformly as it passes two checkpoints that are \(30 \mathrm{~m}\) apart. The time taken between checkpoints is \(4.0 \mathrm{~s}\), and the car's speed at the first checkpoint is \(5.0 \mathrm{~m} / \mathrm{s}\). Find the car's acceleration and its speed at the second checkpoint.

A ball is dropped from rest at a height of \(50 \mathrm{~m}\) above the ground. (a) What is its speed just before it hits the ground? \((b)\) How long does it take to reach the ground? If we can ignore air friction, the ball is uniformly accelerated until it reaches the ground. Its acceleration is downward and is \(9.81 \mathrm{~m} / \mathrm{s}^{2}\). Taking down as positive, we have for the trip: $$y=50.0 \mathrm{~m} \quad a=9.81 \mathrm{~m} / \mathrm{s}^{2} \quad v_{i}=0$$ (a) \(v_{f y}^{2}=v_{i y}^{2}+2 a y=0+2\left(9.81 \mathrm{~m} / \mathrm{s}^{2}\right)(50.0 \mathrm{~m})=981 \mathrm{~m}^{2} / \mathrm{s}^{2}\) and so \(v_{f}=31.3 \mathrm{~m} / \mathrm{s}\). (b) From \(a\left(v_{f y}-v_{i y}\right) / t\), $$t=\frac{v_{f y}-v_{i y}}{a}=\frac{(31.3-0) \mathrm{m} / \mathrm{s}}{9.81 \mathrm{~m} / \mathrm{s}^{2}}=3.19 \mathrm{~s}$$ (We could just as well have taken \(u p\) as positive. How would the calculation have been changed?)

A baseball is thrown straight upward with a speed of \(30 \mathrm{~m} / \mathrm{s}\). (a) How long will it rise? \((b)\) How high will it rise? ( \(c\) ) How long after it leaves the hand will it return to the starting point? ( \(d\) ) When will its speed be \(16 \mathrm{~m} / \mathrm{s} ?\)

An auto's velocity increases uniformly from \(6.0 \mathrm{~m} / \mathrm{s}\) to \(20 \mathrm{~m} / \mathrm{s}\) while covering \(70 \mathrm{~m}\) in a straight line. Find the acceleration and the time taken.

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