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# review%202 - Do you git much work nowadays Jerry Sure LOOK...

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Review for Exam 2 Goran Bregovi ć Ederlezi Ooooh! Did you see the size of that brick? Tush tush! Don’t make so much noise! I know, but it wuz only on your head a second. LOOK OUT! Do you git much work nowadays, Jerry? Sure! I m p u l s e Example: = == = 2 2 1 2 22 ( 9 . 8 m / s ) ( 1 0 m ) 1 4 m / s mgh mv vg h Jiggs is completely missing the point… If the brick has a mass of 1 kg and has been dropped from 10 m, what is the average force on Jerry’s head during the 10 ms it is in contact with his head? Right before hitting Jerry’s head, the speed of the brick is: If the brick is completely stopped by his head, the change in momentum is: ∆= − = = 0 (1 kg)(14 m/s) 14 kg m/s p Therefore, the average force is: == = = ∆∆ average 14 kg m/s 1400 N 0.01 s J F tt Equivalent to 315 lb. Ouch!! 2D (Totally) Inelastic: Sticking Together A. 0 J B. -104 J C. -208 J D. -312 J E. -416 J The two masses in the figure collide and stick together. They are moving on a horizontal, frictionless surface. What is the change in kinetic energy for this process? 5.00 kg 5.00 m/s 10.0 kg 10.0 m/s (Totally) inelastic

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5.00 kg 5.00 m/s 10.0 kg 10.0 m/s AFTER BEFORE 22 2 2 11 1 (15)(1.67 6.67 ) (10)(10 ) (5)(5 ) 208 J 2 KE ∆= =  =+ −+ =   x y ( ) TOTAL, BEFORE TOTAL, AFTER ˆ ˆ (5 kg)( 5 m/s) (10 kg)(10 m/s) (15 kg) ˆ ˆ 1.67 6.67 m/s p i j v vi = = =− + GG G G The two masses in the figure collide and stick together. They are moving on a horizontal, frictionless surface. What is the change in kinetic energy for this process? Example: Elastic collision A. 2.0 m/s, 10 m/s B. 5.3 m/s, 2.7 m/s C. -5.3 m/s, 2.7 m/s D. -3.3 m/s, 2.7 m/s E. -3.3 m/s, 4.7 m/s What is the velocity of each block if the collision is elastic? 1 = 10 m/s 2 = 2.0 m/s 1 kg 5 kg Before mv ′′ +=+ () 12 vv −= −− 1 = 10 m/s 2 = 2.0 m/s 1 kg 5 kg Before 1 2 1 kg 5 kg After 10 10 5 10 2 − − 20 5 8 8 20 5 8 2 28 4.7 m/s 6 == Answer: E 1 3.3 m/s ′=− Example: Cylinder & pulley A 3.00-kg box is suspended from a light rope that passes over a pulley (2.00 kg, radius 20.0 cm) and is wrapped around a cylinder (5.00 kg, radius 40.0 cm). There is no friction between the rope and the pulley or the cylinder. The box is released from rest. Find the speed of the box when it has fallen 1.50 m. cylinder pulley box A. 3.69 m/s B. 4.92 m/s C. 7.69 m/s D. 8.93 m/s E. 9.82 m/s
A 3.00-kg box is suspended from a light rope that passes over a pulley (2.00 kg, radius 20.0 cm) and is wrapped around a cylinder (5.00 kg, radius 40.0 cm). There is no friction between the rope and the pulley or the cylinder. The box is released from rest. Find the speed of the box when it has fallen 1.50 m.

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review%202 - Do you git much work nowadays Jerry Sure LOOK...

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