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P2207_fall10_lecture10

# P2207_fall10_lecture10 - has a 4 grade • How can you keep...

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Today: Forces Solving force problems Why do tennis nets sag?

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m F pull = mg =m*10m/s 2 a=? a=? A. 0 B. g C. >g D. insufficient information
m m m 3 1 2 T 1 / T 3 =? A. 1/3 B. 1/2 C. 1 D. 2 E. 3

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• The Powder River Basin is one of the world’s largest coal producing region. 200 miles of coal trains leave the Powder River Basin every day, 365 days a year, bound for electricity generating plants. • Trains can be up to 2 miles long , and weigh 23,000 tons . Air drag from head winds can reduce an empty train’s speed on level ground from 50 to 20 mph.

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m m m 3 1 2 F F In both cases, T 1 /T 3 = 3 If we add more masses, eventually rope 1 will break. a=0 No friction
• A steep railroad grade is 1.5% • (= 15 feet rise/1000 feet) • The steepest mainline track in the U.S.

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Unformatted text preview: has a 4% grade. • How can you keep the couplers between cars from breaking? (Couplers on coal trains break routinely.) Front… …end of train: locomotive in remote control mode m 1 m 2 frictionless pulley a=? a=? A. 0 B. g C. m 1 g / (m 1 + m 2 ) D. m 2 g / (m 1 + m 2 ) E. (m 1- m 2 ) g / (m 1 + m 2 ) frictionless surface Why do Tennis Nets Sag? m T T T=? A. mg / 2 B. mg /sin( ) C. mg / cos( ) D. mg / 2 sin( ) E. mg / 2 cos( ) m T T T ? A. 0 B. mg / 2 C. mg D. 2mg E. As 0 (i.e., the ropes approach horizontal), T ? Other Applications • sag of power lines • power line and pole snapping by trees, ice • plucking of guitar strings • retrieving your car from a ditch...
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P2207_fall10_lecture10 - has a 4 grade • How can you keep...

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