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Unformatted text preview: h balls start from a 1 m height the baseball the golf ball PHYS115 - Fall 2012 3/8 Test 2 - November 28, 2012 Question 6 – The baseball’s coefficient of restitution is 0 .55. How fast is the baseball after the bat hit it? a.
d. 80 km/h 230 km/h 120 km/h 210 km/h 80 km/h 120 km/h speed = ? 120 km/h
m ANSWER: Argue as in book page 106/107. Collision speed is 120 + 80 = 200 km/h. Coeff. of rest. is 0 .55 so separation speed is 0.55 x 200 = 110 km/h. Add bat speed of 120 km/h to get 110 + 120 = 2 30 km/h. Question 7 – Spinning satellites are particularly stable. S uppose that the astronauts launching a particular satellite decide to increase its angular velocity by a factor of 5. The angular momentum of the satellite is then … a. … 25 times smaller b. … 5 times smaller c. … 5 times larger d. … unchanged ANSWER: Angular momentum is (rotational mass) (angular speed) , so if angular speed gets 5x bigger, so does the angular momentum. spinning
Earth satellite PHYS115 - Fall 2012 4/8 Test 2 - November 28, 2012 Question 8 – The driver is braking because she is approaching a stop sign. In which direction is her apparent weight? ( d) (a ) a.
d. direction (a) direction (b) (c)
direction (c) direction (d) ANSWER: Braking means her (forward) velocity gets smaller, so th e acceleration is backward (as in (d)). The feeling of acceleration is then forward, as in (a). You must add the weight, which points down. Head‐to‐tail addition of forward vector plus dow n vector gives vector (b). Question 9 – The file cabinet slides to the right. (
What frictional force( s) act on it? a.
d. both a static an d a sliding frictional force, to the right a sliding fricti onal force, to the left a static friction al force, to the left a sliding fricti onal force, to the right ANSWER: Because the cabinet slides the friction must be sliding fric tion, not static. The motion is to the right, and friction tends to stop the motion. This gives a force in the opposite direction of the ve...
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