# webct6 - baseball 1. A baseball has a mass m = 0.145 kg....

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baseball 1. A baseball has a mass m = 0.145 kg. The pitched ball has a speed v o = 45 m/s and the velocity of the batted ball is v f = 55 m/s in the opposite direction. Find the magnitude of the change in momentum (in kg m/s) of the ball. Let us take the positive direction in the initial direction of the ball. Then, v o = 45 m/s and v f = –55 m/s. Thus, the change in momentum is fi (0.145 kg)( 55 m/s 45 m/s) 14.5 kg m/s pm v m v ∆= = =− The magnitude of the change in momentum is 14.5 kg m/s. 2. Find the magnitude of the impulse (in N/s) applied to it by the bat. The impulse is equal to the change in momentum, so 14.5 kg m/s. 3. If the ball remains in contact with the ball for 2.00 ms, what is the magnitude of the average force (in N) applied by the bat? net 14.5 kg m/s 7250 N 0.002 s p F t == =

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U(x) 1. The following potential energy function U ( x ) is associated to a force F that acts upon an object of mass m = 3.0 kg. At x = 2.0 m, the x -component of the force is: *a. Positive. b. Negative. c. Zero. The force is minus the derivative of the potential energy, x U F x =− , or minus the slope of the U ( x ) curve. At x = 2.0 m ,the slope is negative. Hence F x is positive. As a rule of thumb, the force always points in the direction of decreasing potential energy. 2. At x = 9.0 m, the x -component of the force is: a. Positive. b. Negative. *c. Zero.
At x = 9 m , the curve is flat, so the slope is zero. 3. Find the work done by force F when the particle moves from x = 4.0 m to x = 8.0 m. For a conservative force (ie, a force that can be associated to a potential energy function), WU =−∆ . Thus, [ ] 4 m to 8 m (8 m) (4 m) (30 J 0) 30 J xx U == =− For the following questions, assume that the object is initially at rest at x = 2.0 m.

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## This homework help was uploaded on 03/26/2008 for the course PHYS 221 taught by Professor Herrera-siklody during the Spring '08 term at Iowa State.

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webct6 - baseball 1. A baseball has a mass m = 0.145 kg....

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