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**Unformatted text preview: **4/25/08 10:23 AM Ch2 HW2 S2008 Page 1 of 7 http:[email protected][email protected] Ch2 HW2 S2008 (Homework) KRISTIN SEILOFF PHYS 2211 M & N Spring 08, section N05, Spring 2008 Instructor: Jennifer Curtis Description Updating position if momentum is changing; Constant force; Graphs of motion Instructions Reading: Sec 2.4-2.5 Because problems 2 and 5 require a long chain of calculations, six submissions are permitted for these problems. For problem 1 (multiple choice), only two submissions are permitted. Web Assign Current Score: 24 out of 24.5 Due: Wednesday, January 23, 200809:05 AM EST 1. 1/1 points | 2/2 submissions The x component of the momentum of an object is observed to increase with time: At t = 0 s, = 30 kg·m/s At t = 1 s, = 40 kg·m/s At t = 2 s, = 50 kg·m/s At t = 3 s, = 60 kg·m/s What can you conclude about the x component of the net force acting on the object during this time? (_) (_) is zero. (_) (_) Not enough information is given. (_) (_) is decreasing with time. (_) (_) is increasing with time. (o) (o) is constant. 2. 4.5/4.5 points | 5/6 submissions A ping-pong ball whose mass is 0.0027 kg ( 2.7 g) is acted upon by the Earth and the air (there is air resistance, and there is also a strong wind). This table gives the position of the ball at several times: Time Position 12.35 s < 3.17 , 2.54 , -9.38 > m 12.39 s < 3.25 , 2.50 , -9.40 > m ... ... 14.35 s < 9.57 , -0.96 , -10.40 > m 14.39 s < 9.75 , -1.06 , -10.42 > m What was the average momentum of the ball during the earlier time interval, from t = 12.35 s to 12.39 s? = < 0.0054 0.0054 , -0.0027 4/25/08 10:23 AM Ch2 HW2 S2008 Page 2 of 7 http:[email protected][email protected] , -0.00135-0.00135 > kg·m/s What was the average momentum of the ball during the later time interval, from t = 14.35 s to 14.39 s? = < 0.01215 0.0121 , -0.00675-0.00675 , -0.00135-0.00135 > kg·m/s In the time interval from 12.35 s to 14.35 s, what was the average net force acting on the ball? = < 0.00336 0.00337 , -0.00203-0.00203 , 0 > N 3. 2/2 points | 4/4 submissions (a) A runner starts from rest and in 3 s reaches a speed of 9 m/s. If we assume that the speed changed at a constant rate (constant net force), what was the average speed during this 3 s interval?...

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