Physics+_Dynamics_answers

Physics+_Dynamics_answers - 2011 Physics+ : Dynamics...

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2011 Physics+ : Dynamics Solution 1. By Newton’s 2 nd law, the resultant upward force on the crate is ma mg T F y = - = , where T is the tension in the cable, and a is the acceleration of the crate. So, the maximum acceleration is 2 max max s m 2 . 15 81 . 9 20 500 - = - = - = g m T a . 2. (a) F net = 0 Truck: T mg sin θ f t = 0 T = (8000)(9.81)(0.025) + 2400 = 4362 4400 N (b) Engine: F tract T mg sin θ f e = 0 F tract = 4362 + (40000)(9.81)(0.025) + 18000 = 32172 32000 N (c) F net = ma Whole system: 60000 – 2400 – 18000 = (8000 + 40000) a a = 0.825 0.83 m s -2 (d) Truck: T – 2400 = (8000) (0.825) T = 9000 N 3. The resultant forces on the mass in the x and y directions are: ma T F x = = θ sin and 0 cos = - = mg T F y (a) So, mg ma T T = cos sin = tan - 1 (0.1) = 5.71 ° (b) Tension, mg mg T 005 . 1 ) 71 . 5 cos( = = 4. “An object will always move in the direction of the resultant force acting on it.” Comment on this statement. The statement is false. There is no connection between an object’s velocity and
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Physics+_Dynamics_answers - 2011 Physics+ : Dynamics...

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