PHY 120 Diablo Valley College Zero Instantaneous Speed Physics Test 3

PHY 120

Diablo Valley College


Question Description

This test includes Fluids, Oscillations and Waves, Sound. Please remember to write the formula.

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LAST NAME:……………………………………………………… First Name:………………………………………………………… DATE: Wednesday April 29, 2020 Spring 2020 PHYS 120 Test 3 Instructions: • Show all work to receive full credit. Answers with insufficient supporting work will receive little or no credit. • Please enter your answer int the space provided. • Please BOX your FINAL ANSWER. Question # Maximum Points Student Score 1 9 2 6 3 11 4 6 5 10 1 6 8 Total Points 50 1. [9 Points] Adult humans are able to exhale a volume of air of about 1.5 × 10−3 m3 (1.5 liters) in 1.0 second. a. Suppose you exhale this volume of air through a straw with radius 0.40 cm. Calculate the speed of the air as it leaves the straw. the straw. (3 pts) 𝑣 = _____________________m/s b. Since the air leaves flows horizontally over the second straw, calculate the difference in pressure between the pressure in the room (𝑃1 ) and the pressure at the top of the second straw (𝑃2 ). Notice that the speed of the air in the rest of the room is zero. Also, you are given that the density of air 𝑘𝑔 is 𝜌𝑎𝑖𝑟 = 1.29 𝑚3. (3 pts) 𝑃1 − 𝑃2 = __________________ N/m2. 𝑘𝑔 c. Calculate the height the water rises to as shown in the figure. Remember that 𝜌𝑤𝑎𝑡𝑒𝑟 = 1000 𝑚3. (3 pts) ℎ = ________________m 2 2. [6 Points] A block of mass m = 1.4 kg is attached to a spring with a force constant k = 370 N/m. The block is in simple harmonic motion. At the moment that the block has zero instantaneous speed, the magnitude of the force acting on it is F = 15 Newtons. a. Find the maximum speed of the block during the vibrations. (3 points) 𝑣𝑚𝑎𝑥 =______________m/s b. Find the magnitude of the net force acting on the block at the moment when the speed is one-half of the maximum speed. (3 points) 𝐹 = ________________N 3 3. [11 Points] The position vs. time for a mass on a spring is shown in the figure below. The attached mass is 8 kg (8.000 kg to be more accurate). a. What is the amplitude of these oscillations? Use the graph shown to answer this. (1 pt) 𝐴 = _____________________m b. What is the period of these oscillations? Use the graph shown to answer this. (1 pt) 𝑇 = _____________________s c. Calculate the angular frequency of oscillations. (1 pt) 𝜔 = _________________rad/s d. Calculate the force constant of the spring. (2 pts) 𝑘 = _________________N/m e. Calculate the total mechanical energy stored this mass-spring system. (2 pts) 𝐸 = __________________J f. What is the position of the mass when 𝑡 = 4 seconds? (2 pts) 𝑥 = __________________m g. What is the velocity of the mass when 𝑡 = 4 seconds? (2 pts) 𝑣 = __________________m 4 4. [6 Points] Two simple pendulums of lengths 𝐿1 = 𝐿 = 0.9 meters and 𝐿2 = 0.64𝐿 = 0.576 meters are suspended from a ceiling. Both pendulums are gently pulled sideways so that the strings are parallel to each other (the side view of this situation is shown). The pendula are then released simultaneously. The acceleration due to gravity is 9.80 m/s2. a. Calculate the period for the pendulum of length 𝐿1 . (2 pts) 𝑇1 = ______________s b. Calculate the period for the pendulum of length 𝐿2 . (2 pts) 𝑇2 = ______________s c. How long would it be before the pendula both simultaneously come back to the position shown in the diagram? (2 pts) 𝑡 = ________________s 5 5. [10 Points] You take 5 m of wire that has a mass of 4 grams and use it to set up a system of standing wave patterns. You tie one end of the wire to a post on your lab bench, 4 meters of the wire runs horizontally to a pulley, and after the pulley the remaining meter of wire is used to support a 1.5 kg hanging mass. Now, an apparatus is used to cause the wire between the post and the pulley to vibrate with a frequency such that 6 bumps in the standing wave pattern are seen. A sketch of the wave pattern is shown below: a. Calculate the mass per unit of length for the given wire. (2 points) 𝜇 = ___________________kg/m b. Calculate the Tension of the wire. (2 points) 𝑇 = _________________N c. Calculate the speed of waves in this wire under tension. (2 points) 𝑣 = __________________m/s d. Calculate the wavelength of the standing waves generated in the above wire. (2 points) 𝜆 = __________________m e. Calculate the frequency used to generate the standing waves in the above wire. (2 points) 𝑓 = _________________Hz 6 6. [8 Points] At 10 meters from a loud rock band you can hear a sound level  = 100 decibels. a. Calculate the intensity 10 meters away from this rock band. (2 points) 𝐼 = _____________________W/m2 b. Calculate the power produced by the rock bands. (2 points) 𝑃 = _____________________W c. How far from the rock band do you have to move in order for  = 0 decibels? (2 points) 𝑟 = __________________m d. If 16 such bands play next to each other, by how much will the sound level () increase? (2 points) The sound level will increase by _________________dB 7 ...
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