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A tennis ball on Mars, where the acceleration due to gravity is \(0.379 g\) and air resistance is negligible, is hit directly upward and returns to the same level \(8.5 \mathrm{~s}\) later. (a) How high above its original point did the ball go? (b) How fast was it moving just after it was hit? (c) Sketch graphs of the ball's vertical position, vertical velocity, and vertical acceleration as functions of time while it's in the Martian air.

Short Answer

Expert verified
The maximum height (h_max) the ball reached is calculated to be: 33.7 m. The initial velocity of the ball just after it was hit is 15.8 m/s. The graphs would illustrate the behavior and properties of the objects motion under gravity.

Step by step solution

01

Calculating Net Time in the Air

Firstly, it is important to note that the total time the ball is in the air, 8.5 seconds, involves both the upward and downward movements. Hence, since these are symmetrical, the time to reach the maximum point (t1) is half of the total time and will be \(t1 = 8.5 s / 2 = 4.25 s\). This is needed for our further calculations.
02

Calculating the Maximum Height

To calculate the maximum height of the ball, we can use the kinematic equation: \(h_{max} = v0 * t1 - 0.5 * g_{Mars} * t1^2\). g_{Mars} is the acceleration due to gravity on Mars and can be calculated as \(g_{Mars} = 0.379 * g = 0.379 * 9.81 ms^-2 = 3.72 ms^-2\). v0 is the initial velocity that we will calculate in the next step.
03

Calculating the Initial Velocity

We can calculate the initial velocity (v0) using the kinematic equation: \(v0 = g_{Mars} * t1\). Substituting the values, we get \(v0 = 3.72 ms^-2 * 4.25 s = 15.8 ms^-1\). Now substitute this value for v0 into the equation in Step 2 to find the maximum height.
04

Sketching the Graphs

Finally, for part (c), sketch the graphs. Keep in mind the following characteristics for each graph: \(Vertical Position vs Time): Parabolic graph, which peaks at \(t1\) and has a maximum height of \(h_{max}\). Vertical Velocity vs Time: A straight line that slopes downward from \(v_0\) to \(-v_0\) at time \(t1\). Vertical Acceleration vs Time: Horizontal line at \(-g_{Mars}\) with no change, indicating that gravity is the only force at play and it remains constant.

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Key Concepts

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

Kinematic Equations
Kinematic equations play a vital role in understanding how objects move. These formulas help us calculate various aspects of an object's motion, such as velocity, position, and time, given constant acceleration. On Mars, as in the tennis ball exercise, we used the kinematic equation \( h_{max} = v0 * t1 - 0.5 * g_{Mars} * t1^2 \) to determine the maximum height the ball reached.

When solving such problems, it's crucial to correctly identify initial conditions and apply the appropriate equation. For example, the initial velocity (\(v0\)) is essential when calculating how high the ball went and how long it was in the air. Since Mars has a different gravitational acceleration than Earth, the kinematic equations will yield results unique to Martian conditions.

Kinematic equations are based on the premise of constant acceleration, so if air resistance or any other force varies during the motion, these equations may need adjustments.
Gravitational Acceleration
Gravitational acceleration is the acceleration on an object caused by the force of gravity. It is denoted as \( g \) on Earth and has a standard value of approximately \( 9.81 m/s^2 \). However, the value of \( g \) varies on different celestial bodies. On Mars, gravitational acceleration is lower because Mars is smaller and has less mass than Earth.

In our exercise, we adjusted Earth's gravitational acceleration to find Mars' value using the equation \( g_{Mars} = 0.379 * g \), leading to \( g_{Mars} = 3.72 m/s^2 \). This change significantly affects how objects move on Mars—in our case, it altered the ball's flight duration and maximum height. Understanding the impact of different gravitational forces is essential for accurate kinematics calculations on any planet.
Projectile Motion
Projectile motion is the movement of an object thrown or projected into the air, subject to only the acceleration of gravity. The path of a projectile is a parabola when air resistance is negligible, like the tennis ball on Mars. Projectile motion can be broken down into two components: horizontal and vertical.

For our Martian tennis ball, the vertical motion is of interest. The exercise showed that the ball's ascending and descending times are equal thanks to the symmetry of projectile motion, allowing us to divide the total time in the air to find the time to reach the maximum height (\( t1 \)). Calculations of projectile motion are essential in predicting where and when objects in motion will land and they help astronauts, engineers, and scientists in planning space missions accurately.
Graphical Analysis of Motion
Graphical analysis is a powerful tool for visualizing an object's motion over time. Graphs can represent how position, velocity, and acceleration change. In our tennis ball example, sketching the position versus time graph would yield a parabola that peaks at \( t1 \). This illustrates how the ball's vertical position increases to a maximum height and then decreases back to the starting level.

The velocity vs. time graph shows a linear change due to constant acceleration - the line slopes downwards, crossing the time axis at \( t1 \) and indicating that the ball stops momentarily at its peak before descending. Meanwhile, the acceleration vs. time graph is a horizontal line that reflects constant gravitational acceleration. Graphs help students visualize and better understand the underlying principles of kinematics, especially when motion becomes complex.

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Most popular questions from this chapter

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