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Ch 09: Work and Kinetic Energy
Chapter 9, Problem 9

A horizontal spring with spring constant 750 N/m is attached to a wall. An athlete presses against the free end of the spring, compressing it 5.0 cm. How hard is the athlete pushing?

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1
Identify the given values: spring constant (k) = 750 N/m, compression distance (x) = 5.0 cm. Convert the compression distance from cm to meters for consistency in units, so x = 0.05 m.
Recall Hooke's Law, which states that the force exerted by a spring is proportional to the displacement from its equilibrium position. The formula is F = -kx.
Substitute the given values into Hooke's Law. Here, F = -750 N/m * 0.05 m.
Calculate the magnitude of the force, ignoring the negative sign which indicates direction (towards the equilibrium position).
The magnitude of the force calculated will tell you how hard the athlete is pushing on the spring.

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Key Concepts

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

Hooke's Law

Hooke's Law states that the force exerted by a spring is directly proportional to its displacement from the equilibrium position, provided the elastic limit is not exceeded. Mathematically, it is expressed as F = -kx, where F is the force, k is the spring constant, and x is the displacement. This principle is fundamental in understanding how springs behave under compression or extension.
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Spring Constant

The spring constant, denoted as k, is a measure of a spring's stiffness. It is defined as the force required to compress or extend the spring by a unit distance. A higher spring constant indicates a stiffer spring that requires more force to achieve the same displacement compared to a spring with a lower spring constant.
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Force Calculation

To determine the force exerted by the athlete on the spring, one can apply Hooke's Law. By substituting the known values of the spring constant and the displacement into the formula F = kx, where k is 750 N/m and x is 0.05 m (5.0 cm), the force can be calculated. This calculation provides insight into the athlete's effort in compressing the spring.
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Related Practice
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Textbook Question
A Porsche 944 Turbo has a rated engine power of 217 hp. 30% of the power is lost in the engine and the drive train, and 70% reaches the wheels. The total mass of the car and driver is 1480 kg, and two-thirds of the weight is over the drive wheels. (b) If the Porsche accelerates at aₘₐₓ, what is its speed when it reaches maximum power output?
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A Porsche 944 Turbo has a rated engine power of 217 hp. 30% of the power is lost in the engine and the drive train, and 70% reaches the wheels. The total mass of the car and driver is 1480 kg, and two-thirds of the weight is over the drive wheels. (c) How long does it take the Porsche to reach the maximum power output?
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