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A \(40.0 \mathrm{~N}\) force stretches a vertical spring \(0.250 \mathrm{~m}\). (a) What mass must be suspended from the spring so that the system will oscillate with a period of \(1.00 \mathrm{~s} ?\) (b) If the amplitude of the motion is \(0.050 \mathrm{~m}\) and the period is that specified in part (a), where is the object and in what direction is it moving \(0.35 \mathrm{~s}\) after it has passed the equilibrium position, moving downward? (c) What force (magnitude and direction) does the spring exert on the object when it is \(0.030 \mathrm{~m}\) below the equilibrium position, moving upward?

Short Answer

Expert verified
The required mass to be hung from the spring is \(0.64 kg\). The object is \(0.021 m\) below the equilibrium position and moving upwards after \(0.35 s\). The force exerted by the spring when the object is \(0.030 m\) below the equilibrium point and moving upward is \(4.8 N\).

Step by step solution

01

Calculation of the Spring's Constant

Firstly, we need to calculate the spring's constant. According to Hooke's law, the force \(F\) applied to a spring equals the product of the spring's constant \(k\) and its displacement \(x\). This can be expressed as \(F = kx\). Given that \(F = 40.0 N\) and \(x = 0.250 m\), we can solve for \(k\) giving us \(k = \frac{F}{x} = \frac{40.0 N}{0.250 m} = 160 N/m.\)
02

Find the Mass

Now, using the formula for the period of a spring-mass system \(T = 2\pi\sqrt{\frac{m}{k}}\), where \(T\) is the period and \(m\) is the mass of the object. We know \(k = 160 N/m\) and the required period \(T = 1.00 s\). Solving for \(m = \frac{(T^2 * k)}{4\pi^2}= \frac{(1.00 s)^2 * 160 N/m}{4\pi^2}= 0.64 kg\). Thus, a mass of \(0.64 kg\) must be hung from the spring.
03

Determine the Position

Moving to part (b), the object's position \(y\) at time \(t\) when it is performing simple harmonic motion domain of amplitude \(A = 0.050 m\) is given by \(y = A * cos(\frac{2\pi t}{T})\), where \(T = 1.00 s\). We need to find \(y\) at \(t = 0.35 s\). Therefore, inserting these values gives \(y = 0.050 m * cos(\frac{2\pi * 0.35 s}{1.00 s}) = -0.021 m\). The negative sign indicates that the object is \(0.021 m\) below the equilibrium position and since it moved downwards to reach there, so it must be moving upwards at \(t = 0.35 s\).
04

Calculate the Force Exerted by the Spring

Lastly, to calculate the force the spring exerts on the object when it is \(0.030 m\) below the equilibrium point and moving upward, use \(F = -k * x\), where \(x = -0.030 m\) because the displacement is downward. So, \(F = -160 N/m * -0.030 m = 4.8 N\). The force exerted by the spring is \(4.8 N\) upwards.

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Key Concepts

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

Understanding Hooke's Law
Hooke's Law is a fundamental principle in physics that describes the relationship between the force applied to a spring and the resulting stretch or compression. It states that the force (\f\(F\f\)) needed to extend or compress a spring by some distance (\f\(x\f\)) is proportional to that distance. This can be written as \f\(F = kx\f\), where \f\(k\f\) is the spring constant and represents the stiffness of the spring. The spring constant is a measure of how much force is required to stretch or compress the spring by a unit of length.

For a more thorough understanding, let's consider an exercise where a vertical spring is stretched by a force of \f\(40.0 \text{ N}\f\) resulting in a displacement of \f\(0.250 \text{ m}\f\). Using Hooke's Law, we can determine the spring constant by rearranging the equation to solve for \f\(k\f\): \f\(k = \frac{F}{x} = \frac{40.0 \text{ N}}{0.250 \text{ m}} = 160 \text{ N/m}\f\). This calculation tells us how much resistance the spring provides per meter of stretch, which in turn helps us understand the system's responses to various forces.
Exploring Simple Harmonic Motion
Simple harmonic motion (SHM) is a type of periodic oscillation where the restoring force is directly proportional to the displacement and acts in the opposite direction. This restoring force can be provided by a spring in a spring-mass system, such as the one described in Hooke's Law.

In SHM, objects oscillate about an equilibrium position. The motion is sinusoidal, meaning it can be described using sine or cosine functions. When a mass is attached to a spring, the mass will move back and forth in SHM if it's displaced from its equilibrium position. Imagine a scenario where a mass is suspended from a spring, pulling it down and causing it to stretch. Once released, the mass will bounce up and down, exhibiting SHM. The motion's amplitude, the maximum extent of oscillation, and the period, the time for one complete cycle of motion, are key characteristics of SHM.

Determination in SHM

For example, if a suspended mass causes the spring to oscillate with a period of \f\(1.00 \text{ s}\f\) and an amplitude of \f\(0.050 \text{ m}\f\), and we wish to find the object's position at a particular time (e.g., \f\(0.35 \text{ s}\f\)), we would use the formula \f\(y = A * \text{cos}(\frac{2\text{π} t}{T})\f\). By plugging in the values, we can determine the object’s position, which informs us about the phase of its oscillation.
Calculating the Oscillation Period
The oscillation period of a spring-mass system represents the amount of time it takes for the mass to complete one full cycle of motion. It is a crucial concept in understanding oscillatory systems and is directly related to the properties of the spring and the mass attached to it.

The formula for the period (\f\(T\f\)) of a spring-mass system is \f\(T = 2\text{π}\text{\text{√}\f{(\frac{m}{k}})}\f\), where \f\(m\f\) is the mass of the object in kilograms and \f\(k\f\) is the spring constant. This shows that the period is independent of the amplitude of oscillation – it depends only on the mass and the spring constant.

Case Study

Let's return to our exercise and apply this concept. Given a spring constant (\f\(k\f\)) of \f\(160 \text{ N/m}\f\) and a desired oscillation period of \f\(1.00 \text{ s}\f\), we can determine the required mass by rearranging the formula: \f\(m = \frac{(T^2 * k)}{4\text{Ï€}^2}= \frac{(1.00 \text{ s})^2 * 160 \text{ N/m}}{4\text{Ï€}^2}= 0.64 \text{ kg}\f\). This calculation demonstrates the relationship between the mass, spring constant, and the period of oscillation in a spring-mass system, and it allows us to design or adjust the system to achieve a particular period of motion.

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Most popular questions from this chapter

A block of mass \(m\) is undergoing SHM on a horizontal, frictionless surface while attached to a light, horizontal spring. The spring has force constant \(k\), and the amplitude of the \(\mathrm{SHM}\) is \(A\). The block has \(v=0,\) and \(x=+A\) at \(t=0 .\) It first reaches \(x=0\) when \(t=T / 4\) where \(T\) is the period of the motion. (a) In terms of \(T,\) what is the time \(t\) when the block first reaches \(x=A / 2 ?\) (b) The block has its maximum speed when \(t=T / 4\). What is the value of \(t\) when the speed of the block first reaches the value \(v_{\max } / 2 ?\) (c) Does \(v=v_{\max } / 2\) when \(x=A / 2 ?\)

A block of mass \(m\) is undergoing SHM on a horizontal, friction less surface while attached to a light, horizontal spring. The spring has force constant \(k,\) and the amplitude of the motion of the block is \(A\). (a) The average speed is the total distance traveled by the block divided by the time it takes it to travel this distance. Calculate the average speed for one cycle of the SHM. (b) How does the average speed for one cycle compare to the maximum speed \(v_{\max } ?\) (c) Is the average speed more or less than half the maximum speed? Based on your answer, does the block spend more time while traveling at speeds greater than \(v_{\max } / 2\) or less than \(v_{\max } / 2 ?\)

A small sphere with mass \(m\) is attached to a massless rod of length \(L\) that is pivoted at the top, forming a simple pendulum. The pendulum is pulled to one side so that the rod is at an angle \(\theta\) from the vertical, and released from rest. (a) In a diagram, show the pendulum just after it is released. Draw vectors representing the forces acting on the small sphere and the acceleration of the sphere. Accuracy counts! At this point, what is the linear acceleration of the sphere? (b) Repeat part (a) for the instant when the pendulum rod is at an angle \(\theta / 2\) from the vertical. (c) Repeat part (a) for the instant when the pendulum rod is vertical. At this point, what is the linear speed of the sphere?

A thin metal disk with mass \(2.00 \times 10^{-3} \mathrm{~kg}\) and radius \(2.20 \mathrm{~cm}\) is attached at its center to a long fiber (Fig. \(\mathbf{E 1 4 . 4 0}\) ). The disk, when twisted and released, oscillates with a period of \(1.00 \mathrm{~s}\). Find the torsion constant of the fiber.

In a physics lab, you attach a \(0.200 \mathrm{~kg}\) air-track glider to the end of an ideal spring of negligible mass and start it oscillating. The elapsed time from when the glider first moves through the equilibrium point to the second time it moves through that point is \(2.60 \mathrm{~s}\). Find the spring's force constant.

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