Unformatted text preview: e) = mass x g(Earth)/10 = 3 x 9.81/10 = close to 3 N 0 7. In the demonstration on the right, a spherical reservoir has small holes. When the reservoir is filled with water under pressure, water squirts out equally in all directions (all beams squirting with the same initial speed). What does this demonstration illustrate? a. Pascal’s Principle b. Hooke’s Law c. Newton’s First Law of Motion d. Bernoulli's Equation 8. 500 a. 1,000,000 Pa b. 267,000 Pa PHYS115 – Spring 2012 4 Final Test - 1 May 2012 c. 333,000 Pa d. 120,000 Pa A: Use ideal gas law p = (N/V) x k x T The number of air molecules N and the volume of the cy linder V don’t change. then p goes up/down only with the rising/falling of the temperature Temperature rises by a factor of 500/300 = 1.666667. Pressure goes up by the same factor, so goes from 200,00 0 to 1.666667 x 200,000 = 333,333 Pa 9. Your 7‐kg rifle fires a 8‐gram (0.008 kg) bullet forward with muzzle velocity 900 m/sec. The rifle recoils in your arms backward at
a. (8 103 ) 9002 30.4 m/s 7 900
b. 129 m /s 7 (8 10 3 ) 900 1.03 m/s c.
7 d. (8 10 3 ) 900 0.0907 m/s 7 v
A: Momentum is zero before the shot, and it’s a conserv ed quantity so it must remain zero, also after the shot. After shot the momentum of the bullet is p(bullet) = mass(bullet) x speed(bullet) (and this is for ward) p
and the momentum of the rifle is mass(rifle) x recoil sp eed(rifle) (and this is backward) The sum of these “new” momenta must still be equal to zero, which it was before the shot.
mass(bullet) x speed(bullet) – mass(rifle) x recoil spe ed(rifle) = 0 8x10–3 x 900 – 7 x recoil speed = 0 so recoil speed 10. (8 10 3 ) 900 1.03 m/s 7 PHYS115 – Spring 2012 5 Final Test - 1 May 2012 A: use ideal gas law p = (N/V) x k x T pressure remains the same: 100,000 Pa (balloon is still in the atmosphere) N remains the same because no air is supposed to enter or leave the balloon So we get p(constant) = N(constant) x k(constant) x T /V and so V goes up/down in sync with temperature going up/down now heater off T goes down volume V goes down...
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