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Work and Energy Quiz Show your work on a separate sheet of paper and staple your work to the back.

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**1. A 2 kg ball is attached to a 0**

1. A 2 kg ball is attached to a 0.80 m string and whirled in a horizontal circle at a constant speed of 6 m/s. The work done on the ball during each revolution is: (A) zero (B) 90 J (C) 72 J (D) 16 J (E) 450 J (A) because F is toward the center and motion is tangential which means force and motion are perpendicular to each other and therefore no work is done.

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2. A force of 30.0 N pushes a 1.5-kg cart, initially at rest, a distance of 2.8 m along a frictionless surface. What is the change in kinetic energy? (A) 126 J (B) 20 J (C) 56 J (D) 84 J (D) Change in kinetic is equal to work (W=Fd)

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**3. A bike and rider, 82. 0-kg combined mass, are traveling at 4. 2 m/s**

3. A bike and rider, 82.0-kg combined mass, are traveling at 4.2 m/s. A constant force of –140 N is applied by the brakes in stopping the bike. What braking distance is needed? (A) 1.23 m (B)101 m (C) 5.2 m (D) 7.3 m © Fd=mv2/2….solve for d

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4. A skier starts from rest at the top of a 60-m hill, skis down a 30° incline into a valley, and continues up a 40-m-high hill. Both hill heights are measured from the valley floor. Assume that you can neglect friction and the effect of ski poles. What is the skier’s speed at the top of the next hill? (A) 20 m/s (B) 15 m/s (C) 10 m/s (D) 5 m/s (A) Conservation of energy equation….initial kinetic is zero, so PEi = Kef + Pef… expand that out and solve for final v.

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**5. A 15-kg bowling ball hangs from the end of a 3-m rope**

5. A 15-kg bowling ball hangs from the end of a 3-m rope. The ball is pulled back until the rope makes a 45° angle with the vertical. What is the gravitational potential energy of the ball? A. 132 J B. 117 J C. 105 J D. 84 J E. 56 J (A) Draw a horizontal from the bowling ball on the left to intersect the ball hanging straight down. Use geometry to calculate height and then calculate PE= mgh

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Recovery Points: Show your work on separate paper and write your answer on this paper. 6. A 15-g bullet is fired horizontally into a kg block of wood suspended by a long cord. The bullet sticks in the block. Compute the velocity of the bullet if the impact causes the block to swing 10 cm above its initial level. 284…see my website for video

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Recovery Points: Show your work on separate paper and write your answer on this paper. 7. An average force of 8.2 N is used to pull a 0.40-kg rock, stretching a sling shot 43 cm. The rock is shot downward from a bridge 18 m above a stream. What will be the velocity of the rock just before it enters the water? 19.4 (not 18.97)….see my website for video

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Example: A 20 kg block is fired horizontally across a frictionless surface. The block strikes a platform that is attached to a spring at its equilibrium.

Example: A 20 kg block is fired horizontally across a frictionless surface. The block strikes a platform that is attached to a spring at its equilibrium.

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