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Ch 02: Motion Along a Straight Line
Chapter 2, Problem 2

(a) If a flea can jump straight up to a height of 0.440 m, what is its initial speed as it leaves the ground?

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Identify the relevant kinematic equation for uniformly accelerated motion that relates initial velocity, acceleration, and displacement. The appropriate equation here is: \( v_f^2 = v_i^2 + 2a\Delta x \), where \( v_f \) is the final velocity, \( v_i \) is the initial velocity, \( a \) is the acceleration, and \( \Delta x \) is the displacement.
Set the final velocity \( v_f \) to zero, since the flea comes to a temporary stop at the peak of its jump.
Recognize that the acceleration \( a \) is due to gravity, which should be taken as \( -9.8 \, \text{m/s}^2 \) (negative because it acts downward while the flea jumps upward).
Substitute the known values into the equation: \( 0 = v_i^2 - 2(9.8)(0.440) \).
Solve the equation for \( v_i \) (initial velocity) by isolating \( v_i \) on one side of the equation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Kinematic Equations

Kinematic equations describe the motion of objects under constant acceleration. In this case, we can use the equation that relates initial velocity, final velocity, acceleration, and displacement to find the initial speed of the flea. The relevant equation is v^2 = u^2 + 2as, where v is the final velocity (0 m/s at the peak), u is the initial velocity, a is the acceleration (due to gravity), and s is the height (0.440 m).
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Acceleration due to Gravity

Acceleration due to gravity is the rate at which an object accelerates towards the Earth when in free fall, approximately 9.81 m/s². This value is crucial for calculating the initial speed of the flea as it jumps, as it will decelerate at this rate until it reaches its maximum height. Understanding this concept allows us to apply the correct value in our kinematic equations.
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Projectile Motion

Projectile motion refers to the motion of an object that is thrown or projected into the air, subject to the force of gravity. In this scenario, the flea's jump can be analyzed as a vertical projectile motion, where the only force acting on it after takeoff is gravity. This concept helps in understanding how the initial speed affects the maximum height achieved during the jump.
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Related Practice
Textbook Question
At the instant the traffic light turns green, a car that has been waiting at an intersection starts ahead with a constant acceleration of 2.80 m/s2. At the same instant a truck, traveling with a constant speed of 20.0 m/s, overtakes and passes the car. (b) How fast is the car traveling when it overtakes the truck?
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Textbook Question
You throw a glob of putty straight up toward the ceiling, which is 3.60 m above the point where the putty leaves your hand. The initial speed of the putty as it leaves your hand is 9.50 m/s. (b) How much time from when it leaves your hand does it take the putty to reach the ceiling?
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Textbook Question
You throw a small rock straight up from the edge of a highway bridge that crosses a river. The rock passes you on its way down, 6.00 s after it was thrown. What is the speed of the rock just before it reaches the water 28.0 m below the point where the rock left your hand? Ignore air resistance.
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Textbook Question
(b) If a flea can jump straight up to a height of 0.440 m, How long is it in the air?
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Textbook Question
A juggler throws a bowling pin straight up with an initial speed of 8.20 m/s. How much time elapses until the bowling pin returns to the juggler's hand?
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Textbook Question
A tennis ball on Mars, where the acceleration due to gravity is 0.379g and air resistance is negligible, is hit directly upward and returns to the same level 8.5 s later. (a) How high above its original point did the ball go?
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