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Ch 5 v1

# Ch 5 v1 - Questions W denotes answer available in Student...

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Questions W denotes answer available in Student Solutions Manual/Study Guide; O denotes objective question 1. A ball is held in a person’s hand. (a) Identify all the external forces acting on the ball and the reaction to each. (b) If the ball is dropped, what force is exerted on it while it is falling? Identify the reaction force in this case. (Ignore air resistance.) 2. If a car is traveling westward with a constant speed of 20 m/s, what is the resultant force acting on it? 3. O An experiment is performed on a puck on a level air hockey table, where friction is negligible. A con- stant horizontal force is applied to the puck and its ac- celeration is measured. Now the same puck is trans- ported far into outer space, where both friction and gravity are negligible. The same constant force is ap- plied to the puck (through a spring scale that stretches the same amount) and the puck’s acceleration (relative to the distant stars) is measured. What is the puck’s ac- celeration in outer space? (a) somewhat greater than its acceleration on the Earth (b) the same as its accel- eration on the Earth (c) less than its acceleration on the Earth (d) infinite because neither friction nor gravity constrains it (e) very large because acceleration is in- versely proportional to weight and the puck’s weight is very small but not zero 4. In the motion picture It Happened One Night (Columbia Pictures, 1934), Clark Gable is standing in- side a stationary bus in front of Claudette Colbert, who is seated. The bus suddenly starts moving forward and Clark falls into Claudette’s lap. Why did that happen? 5. Your hands are wet and the restroom towel dis- penser is empty. What do you do to get drops of water off your hands? How does your action exemplify one of Newton’s laws? Which one? 6. A passenger sitting in the rear of a bus claims that she was injured when the driver slammed on the brakes, causing a suitcase to come flying toward her from the front of the bus. If you were the judge in this case, what disposition would you make? Why? 7. A spherical rubber balloon inflated with air is held stationary, and its opening, on the west side, is pinched shut. (a) Describe the forces exerted by the air on sections of the rubber. (b) After the balloon is re- leased, it takes off toward the east, gaining speed rap- idly. Explain this motion in terms of the forces now acting on the rubber. (c) Account for the motion of a skyrocket taking off from its launch pad. 8. If you hold a horizontal metal bar several centi- meters above the ground and move it through grass, each leaf of grass bends out of the way. If you increase the speed of the bar, each leaf of grass will bend more quickly. How then does a rotary power lawn mower manage to cut grass? How can it exert enough force on a leaf of grass to shear it off?

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