/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 63 A physics professor did daredevi... [FREE SOLUTION] | 91Ó°ÊÓ

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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. \(\mathbf{P 3 . 6 3 )}\). 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. 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 part (a), where did he land?

Short Answer

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Answers: (a) For the professor to just make it to the edge of the far bank, his speed at the top of the ramp should have been calculated from our final equation in step 4. (b) If his speed was only half the value found in part (a), he landed at the distance calculated using the equation in step 5.

Step by step solution

01

Identifying Given Variables

Let's comprehend the problem and identify the variables provided: The angle of projection, \(\theta = 53.0^\circ\), the horizontal displacement or range, \(R = 40.0 m\), and the vertical displacement or height, \(h = 15.0 m\). The main aim is to calculate the speed of the motorcycle.
02

Utilizing Initial Vertical Velocity

Start by finding the time it takes to reach the maximum height by using the equation: \(t_{up} = \frac{v_{i_y}}{g}\), where \(v_{i_y}\) is the initial vertical speed \(v_{i_y} = v_i \sin(\theta)\) and \(g\) is acceleration due to gravity usually approximated to be \(9.8 m/s^2\). Now, \(t_{up} = \frac{v_i \sin(\theta)}{g}\)
03

Finding Total Time

The projectile motion of the motorcycle is symmetric. This implies that the time it takes to reach the maximum height is the same as the time it takes to descend to the same height again from the top. Hence, the total time can be calculated by multiplying \(t_{up}\) with 2. That gives us: \(t = 2t_{up} = \frac{2v_i \sin(\theta)}{g}\)
04

Solve for Initial Speed

Now, use the total time in the equation of motion for horizontal displacement (range) to solve for initial speed. The equation for range is \(R = v_{i_x} t\), where \(v_{i_x}\) is the initial horizontal speed, \(v_{i_x} = v_i \cos(\theta)\). Replace \(v_{i_x}\) in the range equation, to find the initial speed. We end up with: \(R = v_i \cos(\theta) \frac{2v_i \sin(\theta)}{g}\). Solve this equation to find \(v_i\)
05

Solve Part (b)

For part (b), use \(v_i/2\) as the new initial speed and the equation for range to find out the new distance.

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Key Concepts

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

Angle of Projection
Understanding the angle of projection is crucial in analyzing projectile motion physics. The angle of projection, denoted by \( \theta \), is the angle at which an object is launched above the horizontal axis. In the given exercise, the motorcycle's takeoff ramp was inclined at \( 53.0^\circ \) above the horizontal. This angle significantly impacts the projectile's trajectory.

When a projectile is launched at an angle, its initial velocity is split into two components: horizontal (\( v_{i_x} = v_i \cos(\theta) \) and vertical (\( v_{i_y} = v_i \sin(\theta) \) ). The vertical component is affected by gravity, causing the projectile to rise and then fall, while the horizontal component remains constant (ignoring air resistance). The angle of projection helps determine these components and is used to calculate the range and the ideal speed for clearing obstacles, like in the professor's motorcycle stunt.
Initial Velocity Calculation
The initial velocity of a projectile, \( v_i \), is the speed at which it is launched. To calculate the initial velocity in projectile motion, both the magnitude of the speed and the direction of launch must be taken into account. The given problem necessitated calculating the speed the professor needed to safely land on the far bank.

To calculate \( v_i \), you can use the professor's angle of projection and the range required to cross the river, using the formula for range in projectile motion: \( R = v_i \cos(\theta) \frac{2v_i \sin(\theta)}{g} \). By rearranging this formula, you can solve for \( v_i \), which will provide the necessary speed at launch to ensure the motorcycle reaches the desired range. In practical terms, finding the correct initial velocity can mean the difference between a successful stunt and a spectacular failure.
Range of Projectile
The range of a projectile is the horizontal distance it travels before landing. It's an essential concept in projectile motion, representing the effectiveness of the launch angle and initial velocity in determining how far the object will go. If you want to maximize range, you'd typically launch a projectile at a \( 45^\circ \) angle. However, when obstacles are present, like in our physics professor's stunt, other angles might be more appropriate.

The formula \( R = v_{i_x} t \) is used to calculate the range, where \( v_{i_x} \) is the horizontal component of the initial velocity and \( t \) is the time of flight. The initial velocity in each direction is derived from the initial speed and angle of launch. As shown in the exercise, the range can be used to determine whether the professor's motorcycle will clear the river, and if not, where it's likely to land. The calculation provides a predictable outcome for the projectile's path, allowing for informed decisions and precise actions.

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Most popular questions from this chapter

A rookie quarterback throws a football with an initial upward velocity component of \(12.0 \mathrm{~m} / \mathrm{s}\) and a horizontal velocity component of \(20.0 \mathrm{~m} / \mathrm{s}\). Ignore air resistance. (a) How much time is required for the football to reach the highest point of the trajectory? (b) How high is this point? (c) How much time (after it is thrown) is required for the football to return to its original level? How does this compare with the time calculated in part (a) (d) How far has the football traveled horizontally during this time? (e) Draw \(x-t, y-t, v_{x}-t,\) and \(v_{y}-t\) graphs for the motion.

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