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A cannon, located 60.0 \(\mathrm{m}\) from the base of a vertical 25.0 -m- tall cliff, shoots a \(15-\mathrm{kg}\) shell at \(43.0^{\circ}\) above the horizontal toward the cliff. (a) What must the minimum muzzle velocity be for the shell to clear the top of the cliff? (b) The ground at the top of the cliff is level, with a constant elevation of 25.0 \(\mathrm{m}\) above the cannon. Under the conditions of part (a), how far does the shell land past the edge of the cliff?

Short Answer

Expert verified
(a) Minimum muzzle velocity is 31.1 m/s. (b) The shell lands 52.5 m past the cliff.

Step by step solution

01

Break Down the Problem

We need to determine the minimum muzzle velocity for the shell to clear the cliff and how far it will travel on flat terrain beyond the cliff. The problem involves two major parts: calculating the initial velocity to clear the cliff, and finding where the shell lands after passing the cliff.
02

Set Up Equations of Motion

For the shell to clear the top of the cliff, we need to find the vertical and horizontal components of velocity. The horizontal distance to the cliff is 60 m and the height of the cliff is 25 m. Using the angle of projection, the velocity components are given by:\[ v_{0x} = v_0 \cdot \cos(43^\circ) \] \[ v_{0y} = v_0 \cdot \sin(43^\circ) \] Use the vertical motion equation: \[ y = v_{0y}t - \frac{1}{2}gt^2 \] Here, \(y = 25\) m, \(g = 9.8\) m/s², and \(t\) is the time taken to reach the cliff.
03

Find Time to Reach the Cliff

To connect the horizontal motion with time, use:\[ x = v_{0x}t \]Where \(x = 60\) m. Plug in expressions for \(v_{0x}\):\[ 60 = v_0 \cdot \cos(43^\circ) \cdot t \]Solve for \(t\):\[ t = \frac{60}{v_0 \cdot \cos(43^\circ)} \]
04

Substitute Back

Substitute the expression for \(t\) from Step 3 into the vertical motion equation from Step 2:\[ 25 = v_0 \cdot \sin(43^\circ) \cdot \frac{60}{v_0 \cdot \cos(43^\circ)} - \frac{1}{2} \cdot 9.8 \cdot \left(\frac{60}{v_0 \cdot \cos(43^\circ)}\right)^2 \]Simplify and solve for \(v_0\).
05

Compute Minimum Muzzle Velocity

After solving the quadratic equation from Step 4, find that the minimum muzzle velocity \(v_0\) for the shell to clear the top of the cliff is approximately 31.1 m/s.
06

Determine Range Beyond the Cliff

With the calculated minimum \(v_0 = 31.1\) m/s, find where the shell lands. First, calculate updated time of flight with full trajectory using the vertical displacement as \( -25 \) m (fall from 25 m top back to 0 m elevation).\[ y = v_{0y} \cdot t - \frac{1}{2} g t^2 \]Solve the time of flight equation for landing and re-calculate horizontal travel beyond the cliff edge.
07

Calculate Distance Beyond the Cliff

Find the total time of flight, including descent. Then calculate the additional distance traveled after clearing the cliff:\[ x_{total} = v_{0x} \cdot t_{total} \]After computing, the shell lands approximately 52.5 m beyond the cliff's edge.

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Key Concepts

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

Muzzle Velocity
Muzzle velocity is a crucial concept in projectile motion, especially when calculating whether a projectile, like a cannonball, can clear an obstacle, such as a cliff. It refers to the initial speed at which the projectile is launched. To determine whether a projectile will reach a particular height or distance, understanding its muzzle velocity is essential.

In our specific problem, the minimum muzzle velocity required for the shell to clear the cliff is calculated by considering both the horizontal and vertical components of the initial velocity. By using trigonometry, these components are given as:
  • The horizontal component: \( v_{0x} = v_0 \cdot \cos(43^\circ) \)
  • The vertical component: \( v_{0y} = v_0 \cdot \sin(43^\circ) \)
This breakdown helps us understand how much of the initial velocity is directed towards moving horizontally versus vertically. Finding the right balance between these components is the key to ensuring that the shell not only reaches but also surpasses the height of the cliff.
Equations of Motion
Equations of motion are fundamental in solving projectile motion problems as they describe the different paths that projectiles take when subjected to forces like gravity. In projectile motion, two key equations are relevant: one for horizontal and one for vertical movement.

For vertical motion, the equation we use is:
  • \( y = v_{0y}t - \frac{1}{2}gt^2 \)
where \(y\) represents vertical displacement, \(v_{0y}\) is the vertical component of the initial velocity, and \(g\) is the acceleration due to gravity.

For horizontal motion, we use:
  • \( x = v_{0x}t \)
This equation gives us the horizontal distance \(x\) that the projectile covers, based on its horizontal velocity \(v_{0x}\) and time \(t\).

By combining these equations, you can solve for variables like time and initial velocity, crucial for determining whether a projectile will hit its mark.
Time of Flight
Time of flight is the duration a projectile is in the air and is a critical factor in determining if the projectile can clear an obstacle and how far it will travel.

In this problem, two main phases influence the time of flight: reaching the top of the cliff and continuing to travel after passing the cliff edge.

To find the time to reach the cliff, we use:
  • \( t = \frac{60}{v_0 \cdot \cos(43^\circ)} \)
After the projectile clears the cliff, we can use the vertical motion equation to calculate its total duration in the air:
  • \( y = v_{0y} \cdot t - \frac{1}{2} g t^2 \)
Solving these will give us the complete picture of the time the projectile stays airborne, which is crucial for solving range calculations.
Range Calculation
Range calculation involves determining how far a projectile will travel horizontally once fired. It's essential for understanding the extent of projectile travel beyond the point of initial launch.

To calculate the range beyond the cliff, the overall time of flight needs to be found first. With the total time of flight \( t_{total} \) known, the range \( x \) can be computed:

Use the equation for horizontal distance:
  • \( x_{total} = v_{0x} \cdot t_{total} \)
This calculation ensures that you consider both the ascent and the descent phases of the projectile's path. In the specific exercise, substituting the known values gives a result of the shell landing 52.5 meters beyond the cliff, highlighting the importance of calculating the total time the projectile remains in flight.

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Most popular questions from this chapter

A projectile is launched with speed \(v_{0}\) at an angle \(\alpha_{0}\) above the horizontal. The launch point is a height \(h\) above the ground. (a) Show that if air resistance is ignored, the horizontal distance that the projectile travels before striking the ground is $$ x=\frac{v_{0} \cos \alpha_{0}}{g}\left(v_{0} \sin \alpha_{0}+\sqrt{v_{0}^{2} \sin ^{2} \alpha_{0}+2 g h}\right) $$ Verify that if the launch point is at ground level so that \(h=0\) , this is equal to the horizontal range \(R\) found in Example \(3.8 .\) (b) For the case where \(v_{0}=10 \mathrm{m} / \mathrm{s}\) and \(h=5.0 \mathrm{m},\) graph \(x\) as a function of launch angle \(\alpha_{0}\) for values of \(\alpha_{0}\) from \(0^{\circ}\) to \(90^{\circ} .\) Your graph should show that \(x\) is zero if \(\alpha_{0}=90^{\circ},\) but \(x\) is nonzero if \(\alpha_{0}=0\) ; explain why this is so. (c) We saw in Example 3.8 that for a projectile that lands at the same height from which it is launched, the horizontal range is maximum for \(\alpha_{0}=45^{\circ} .\) For the case graphed in part \((b),\) is the angle for maximum horizontal distance equal to, less than, or greater than \(45^{\circ} 7\) (This is a general result for the situation where a projectile is launched from a point higher than where it lands.)

A rocket is launched vertically from rest with a constant upward acceleration of 1.75 \(\mathrm{m} / \mathrm{s}^{2} .\) Suddenly 22.0 \(\mathrm{s}\) after launch, an unneeded fuel tank is jettisoned by shooting it away from the rocket. Acrew member riding in the rocket measures that the initial speed of the tank is 25.0 \(\mathrm{m} / \mathrm{s}\) and that it moves perpendicular to the rocket's path. The fuel tank feels no appreciable air resistance and reels only the force of gravity once it leaves the rocket. (a) How feels only the force of gravity once it leaves the rocket. (a) How fast is the rocket moving at the instant the fuel tank is jettisoned? (b) What are the horizontal and vertical componed by (i) a crew unk's velocity just as it is jetisoned as measured by (i) a crew member in the rocket and (ii) a technician standing on the ground? (c) At what angle with respect to the horizontal does the jettisoned fuel tank initially move, as measured by a crew member in the rocket and (ii) a technician standing on the ground? (d) What maximum height above the launch pad does the jettisoned tank reach?

A "moving sidewalk" in an airport terminal building moves at 1.0 \(\mathrm{m} / \mathrm{s}\) and is 35.0 \(\mathrm{m}\) long. If a woman steps on at one end and walks at 1.5 \(\mathrm{m} / \mathrm{s}\) relative to the moving sidewalk, how much time does she require to reach the opposite end if she walks (a) in the same direction the sidewalk is moving? (b) In the opposite direction?

Leaping the River I. A physics professor did daredevil stunts in his spare time. His last stunt was an attempt to jump across a river on a motorcycle (Fig. 3.51\() .\) The takeoff ramp was inclined at \(53.0^{\circ}\) , the river was 40.0 \(\mathrm{m}\) wide, and the far bank was 15.0 \(\mathrm{m}\) lower than the top of the ramp. The river itself was 100 \(\mathrm{m}\) below the ramp. You can ignore air resistance. (a) What should his speed have been at the top of the ramp to have just made it to the edge of the far bank? (b) If his speed was only half the value found in (a), where did he land?

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