2C1T PHY 121 Fall 2017 Test 3 (Chs 7,8) Open book/notes [Friday, Nov. 17 (PM)] N

Question

2C1T PHY 121 Fall 2017 Test 3 (Chs 7,8) Open book/notes [Friday, Nov. 17 (PM)] Narne: Please write your solutions in the blue books. Show all work in an orderly and legible manner. Use appropriate units and significant figures. Turn in the takehome problem with the test. 1. A ribosome (mass 2.1 million uj stall s on a piece of messenger RNA it has been readine. S mi Another ribosome (m ass 2.5 million u moving at a rate of 55 nucleotides per second comes up from behind and collides with the stalled ribosome. If the collision is elastic (admittedly this is mption-see article on back page for what might actulyhappen) t are the new translation velocities (in nucleotides per second [nt/sl) of the ribosomes? 2.1106 “Steno the cellsion 2. A circular shortwave loop antenna (mass 3.00 kg) has a radius of 0.150 m and a width of 4.00 cm. What magnitude torque is required to spin this antenna about its diameter from rest to 1.00 rev/minute in 2.00 seconds? (Hint: First calculate the rotational inertia.) n 3.cok 3. A uniform narrow plank with a mass of 1350 kg and a length of 5.0 meters spins freely about its center. Two people, each having a mass of 65 kg, initially are standing at the opposite ends of the plank as it spins. The initial angular velocity of this system is 0.25 revolutions/s. If both people walk halfway inwards towards the center at the same time in a radial direction what is the new angular speed (in rev/s) of the rotating system after the people arrive at their new ocations? Axis eete te (pv.er

Explanation / Answer

From law of conservation (momentum and energy conservation) we got the formula

v1' = ((m1-m2 / (m1 + m2)) v1 + ((2m2) / (m1 + m2)) v2

v1' = ((((2.5 x 10^6) - (2.1 x 10^6)) / ((2.5 x 10^6) + (2.1 x 10^6))) x 55) + ((2 x 2.1 x 10^6) / ((2.5 x 10^6) + (2.1 x 10^6))) x 0

v1' = 4.782 nt/s

v2' = ((2m1) / (m1 + m2) x v1) + (((m2 - m1) / (m1 + m2)) x v2)

v2' = (((2 x 2.5 x 10^6) / ((2.5 x 10^6) + (2.1 x 10^6))) x 55 + 0

v2' = 59.78 m/s

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