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A 10.0-kg mass is traveling to the right with a speed of 2.00 m/s on a smooth horizontal surface when it collides with and sticks to a second 10.0-kg mass that is initially at rest but is attached to a light spring with force constant 170.0 N/m. (a) Find the frequency, amplitude, and period of the subsequent oscillations. (b) How long does it take the system to return the first time to the position it had immediately after the collision?

Short Answer

Expert verified
Frequency is 0.465 Hz, amplitude is 0.344 m, period is 2.15 s; it takes 0.538 s to return to the initial position.

Step by step solution

01

Calculate the Velocity after Collision

When the two masses collide and stick together, it is a perfectly inelastic collision. The initial momentum is equal to the final momentum according to the law of conservation of momentum. The formula is:\[ m_1 v_1 + m_2 v_2 = (m_1 + m_2) v_f \]Here, \(m_1 = 10.0\, \text{kg},\) \(v_1 = 2.00\, \text{m/s},\) \(m_2 = 10.0\, \text{kg},\) \(v_2 = 0\, \text{m/s}\). Substituting these values,\[ 10 \times 2 + 10 \times 0 = (10 + 10) v_f \]\[ v_f = 1.00\, \text{m/s} \]
02

Calculate Angular Frequency

The angular frequency of a mass-spring system is given by:\[ \omega = \sqrt{\frac{k}{m}} \]where \(k = 170.0\, \text{N/m}\) is the spring constant, and \(m = 20.0\, \text{kg}\) is the combined mass of both bodies. So,\[ \omega = \sqrt{\frac{170}{20}} = \sqrt{8.5} \approx 2.92\, \text{rad/s} \]
03

Calculate Frequency of Oscillation

The frequency \(f\) is given by the formula:\[ f = \frac{\omega}{2\pi} \]Substituting \(\omega = 2.92\, \text{rad/s},\)\[ f \approx \frac{2.92}{2\pi} \approx 0.465\, \text{Hz} \]
04

Calculate Amplitude

The amplitude \(A\) can be found using conservation of energy, where initially all kinetic after the collision is converted into spring potential energy:\[ \frac{1}{2} m v_f^2 = \frac{1}{2} k A^2 \]Substitute \(m = 20\, \text{kg},\) \(v_f = 1.00\, \text{m/s},\) and \(k = 170\, \text{N/m}\).\[ 20 \times 1^2 = 170 \times A^2 \]\[ A = \sqrt{\frac{20}{170}} \approx 0.344\, \text{m} \]
05

Calculate Period of Oscillation

The period \(T\) of oscillation is the reciprocal of frequency:\[ T = \frac{1}{f} \]Substituting \(f \approx 0.465\, \text{Hz},\)\[ T \approx \frac{1}{0.465} \approx 2.15\, \text{s} \]
06

Time to Return to Initial Position

The time to return to the initial position after the collision corresponds to a quarter of the period because the mass-spring system must move from maximum compression to the equilibrium position.\[ t = \frac{T}{4} \]Substitute \(T \approx 2.15\, \text{s}\).\[ t \approx \frac{2.15}{4} \approx 0.538\, \text{s} \]

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Key Concepts

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

Conservation of Momentum
When dealing with collisions, the conservation of momentum is a fundamental principle that helps us understand the behavior of objects during a collision. Momentum is a measure of an object's motion and is the product of its mass and velocity. During a perfectly inelastic collision, like the one described in the problem, the two colliding objects stick together after the impact. This means their combined mass is now moving with a common velocity post-collision. The law of conservation of momentum states that the total momentum before the collision must equal the total momentum after the collision. This principle allows us to calculate the final velocity of the combined mass. In our scenario, two 10.0 kg masses collide; one is initially moving while the other is at rest. Applying the conservation of momentum:
  • Initial momentum: 10.0 kg × 2.00 m/s + 10.0 kg × 0 m/s = 20.0 kg·m/s
  • Final momentum of the combined mass: (10.0 kg + 10.0 kg) × v_f = 20.0 kg·m/s
Solving gives the final velocity, \(v_f = 1.00 \; \text{m/s}\), confirming the conservation of momentum in action.
Mass-Spring System
A mass-spring system is a classical model used in physics to describe oscillatory motion, often idealized to ignore damping and other forces apart from the restoring force of the spring. In this system, a mass is attached to a spring with a known spring constant, represented by \(k\). Once an initial push or force is applied to this system, it will oscillate back and forth around an equilibrium position. The spring force, according to Hooke's Law, is proportional to the displacement but acts in the opposite direction. This restoring force causes the mass to accelerate back towards equilibrium. In our problem, after the collision, the two masses together act as a single mass of 20.0 kg, attached to the spring with a spring constant of 170.0 N/m. The interaction of the mass with the spring determines the oscillatory behavior of the system, characterized by its frequency, period, and amplitude of oscillation.
Angular Frequency
Angular frequency \(\omega\) is a key parameter in describing oscillatory motion, indicating how fast an object oscillates. In the context of a mass-spring system, it relates to how rapidly the system completes its cycles of movement. The formula to compute the angular frequency for a mass-spring system is: \[\omega = \sqrt{\frac{k}{m}}\]where \(k\) is the spring constant, and \(m\) is the total mass of the system. For our exercise, with a spring constant of 170.0 N/m and a combined mass of 20.0 kg, the angular frequency is calculated as: \[\omega = \sqrt{\frac{170}{20}} \approx 2.92 \; \text{rad/s}\]This value signifies the radians per second at which the system oscillates, providing insight into the system's dynamic properties.
Amplitude of Oscillation
The amplitude of oscillation describes the maximum displacement from the equilibrium position that the system achieves during its motion. It's a measure of how "big" the oscillation is. In a mass-spring system where kinetic and potential energy are exchanged, the amplitude can be determined by utilizing the conservation of energy principle. Immediately after the collision, all kinetic energy is converted into potential energy at the point of maximum displacement: \[\frac{1}{2} m v_f^2 = \frac{1}{2} k A^2\]Using this relation and plugging in values from our exercise (\(m = 20\; \text{kg}\), \(v_f = 1.00\; \text{m/s}\), \(k = 170\; \text{N/m}\)), we solve for the amplitude:\[A = \sqrt{\frac{20}{170}} \approx 0.344 \; \text{m}\]This means the system moves 0.344 meters away from equilibrium at its furthest point during oscillation. Understanding amplitude is crucial as it helps in predicting the extent of oscillation based on initial conditions.

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Most popular questions from this chapter

A 1.50-kg mass on a spring has displacement as a function of time given by $$x(t) = 7.40 \mathrm{cm}) \mathrm{cos} [ (4.16 \mathrm{rad}/s)t - 2.42] $$ Find (a) the time for one complete vibration; (b) the force constant of the spring; (c) the maximum speed of the mass; (d) the maximum force on the mass; (e) the position, speed, and acceleration of the mass at \(t =\) 1.00 s; (f) the force on the mass at that time.

You hang various masses \(m\) from the end of a vertical, 0.250-kg spring that obeys Hooke's law and is tapered, which means the diameter changes along the length of the spring. Since the mass of the spring is not negligible, you must replace \(m\) in the equation \(T =\) 2\(\pi\sqrt{ m/k }\) with \(m + m_\mathrm{eff}\), where \(m_\mathrm{eff}\) is the effective mass of the oscillating spring. (See Challenge Problem 14.93.) You vary the mass m and measure the time for 10 complete oscillations, obtaining these data: (a) Graph the square of the period \(T\) versus the mass suspended from the spring, and find the straight line of best fit. (b) From the slope of that line, determine the force constant of the spring. (c) From the vertical intercept of the line, determine the spring's effective mass. (d) What fraction is \(m_\mathrm{eff}\) of the spring's mass? (e) If a 0.450-kg mass oscillates on the end of the spring, find its period, frequency, and angular frequency.

A 5.00-kg partridge is suspended from a pear tree by an ideal spring of negligible mass. When the partridge is pulled down 0.100 m below its equilibrium position and released, it vibrates with a period of 4.20 s. (a) What is its speed as it passes through the equilibrium position? (b) What is its acceleration when it is 0.050 m above the equilibrium position? (c) When it is moving upward, how much time is required for it to move from a point 0.050 m below its equilibrium position to a point 0.050 m above it? (d) The motion of the partridge is stopped, and then it is removed from the spring. How much does the spring shorten?

A 0.150-kg toy is undergoing SHM on the end of a horizontal spring with force constant \(k =\) 300 N/m. When the toy is 0.0120 m from its equilibrium position, it is observed to have a speed of 0.400 m/s. What are the toy's (a) total energy at any point of its motion; (b) amplitude of motion; (c) maximum speed during its motion?

A 2.00-kg bucket containing 10.0 kg of water is hanging from a vertical ideal spring of force constant 450 N/m and oscillating up and down with an amplitude of 3.00 cm. Suddenly the bucket springs a leak in the bottom such that water drops out at a steady rate of 2.00 g/s. When the bucket is half full, find (a) the period of oscillation and (b) the rate at which the period is changing with respect to time. Is the period getting longer or shorter? (c) What is the shortest period this system can have?

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