MT%20exam%202

MT%20exam%202 - Student name_ Student NID_ PHY 2053C_0001...

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Student name________________________________________ Student NID__________________________________________ PHY 2053C_0001 Midterm exam 2, March 23, 2011, Chapters 4-7 1) ( 2 points ) A sled with people is sliding down the hill, as shown in Figure 1. The total weight of the sled and people in it is w = 250 N, the slope angle is α = 35 o , and there is no friction. Find the acceleration of the sled and the normal force F N . mg sin α = ma x a x = g sin α = 5.6 m/s 2 F N = mg cos α = w cos α = 204.8 N 2) ( 2 points ) Two spheres, with masses m 1 = 0.01 kg and m 2 = 0.50 kg, are held at a distance r = 0.05 m. What would be the accelerations of each sphere at the moment when they are released, a 1 and a 2 , provided they only feel each other’s gravitational force (i.e., you can ignore all other forces). Hint: 3) ( 2 points ) A 0.02-kg ball is shot from the plunger of a pinball machine. Because of a centripetal force of 0.018 N, the ball follows a circular arc whose radius is 0.25 m. What is the speed of the ball? 1 Figure 1 11 2 2 6.674 10 / G N m kg - = × Figure 2 11 2 2 10 1 2 2 2 0.01 0.5 (6.674 10 / ) 1.33 10 0.0025 g m m kg kg F G N m kg N r m - - × = = × = × 10 8 2 1 1 10 10 2 2 2 1.33 10 1.33 10 / 0.01 1.33 10 2.66 10 / 0.50 g g F N a m s m kg F N a m s m kg - - - - × = = = × × = = = × 2 c c v F m r F r 0.018N 0.25m v 0.47m / s m 0.02kg = × = = =
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Student name________________________________________ Student NID__________________________________________
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MT%20exam%202 - Student name_ Student NID_ PHY 2053C_0001...

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