Practice Test  Momentum, Center of Mass (Mr. Rogers AP Physics C ) 


Online Quiz  Momentum 8BBD445C  
1  )  Find the center of mass of a triangular shaped object of length L with the following height = 1.5 L. Assume uniform thickness and density. Show all work. X_{cm} = 2/3 L, Y_{cm} = .5 L 
2  )  A 2 kg mass is located 1.0 m directly above a 1.0 kg mass. A third 3 kg mass is located 2 m directly to the right of the 1.0 kg mass. find the location of the center of mass. X_{cm} = 1.0 m, Y_{cm} = 1/3 m 
3  )  A 0.5 kg bullet hits a 25 kg ballistic pendulum and causes it to rise by 0.5 m. Find the initial velocity of the bullet. V_{b }= 161 m/s 
4  )  At an intersection, a car of mass = 2m and velocity v plows into a car of mass = 3m going through the intersection from a perpendicular direction at the same speed. The cars stick together. Find the final velocity's magnitude. V_{f } = 0.72 m/s 
5  )  A billiard ball collides with another billiard ball. The first ball goes off at an angle of 30 degrees with respect to its original velocity. What is the second ball's angle with respect to the first ball's original velocity. 60 degrees, It's the complement of 30 degrees 
6  ) 
Two objects collide elastically in outer space. During the
collision the force is as follows: F = 25 t^3. The collision lasts 0.5 sec.
What is the magnitude of the change in momentum for each object?
Imp = ∫ F_{(t) } ∙ dt = ∫ 25 t^3∙ dt = 25 (1/4) t^4 = 25 (.25) (.5)^4 = 0.3906 
7  ) 
Coal drops at a rate of 10 kg / sec. on a conveyor belt
moving at 2 m/s. How much force is required to keep the belt moving at
constant velocity? F = dp/dt = V (dm/dt) = (2 m/s) ( 10 kg/s) = 20 N 
8  )  Bob crashes into a tree when he is traveling at 30 m/s. His truck has a mass of 1500 kg. Find the impulse during the collision. 45,000 Ns 
9  )  Is impulse a vector? Yes 
10  )  Does impulse follow Newton's 3rd law? Yes 
11  )  Can Newton's 2nd law be stated in terms of momentum? ΣF = dP/dt 
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