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Chapter 4 Motion and Force: Dynamics 1a. The word "push" is a reasonably good synonym for the word "force." Is "hold" a synonym for force? How about "support?" Can you think of others? 1b. A locomotive pulling a train is accelerating the train on a level track. The tension in the couplings is a.) the same anywhere along the train. b.) least between the locomotive and the first car. c.) least between the last car and the caboose. d.) none of the above. 1c. Consider a car at rest. We can conclude that the downward gravitational pull of the Earth on the car and the upward contact or normal force of the Earth on the car are equal and opposite because a.) the two forces form an interaction pair. b.) the net force on the car is zero. c.) neither of the above. 1d. Are there any thoughts you wish to share, whether they are about this assignment, the reading (what seems impossible, what makes no sense, what you'd like to spend time on in class, what you really found interesting etc) or the course?
2a. Consider a hand holding a ball at rest. The ball weighs 10 N. The forces acting on the ball are its weight and the force of the hand on the ball. The forces acting on the hand are the weight of the hand and the force exerted by the ball on the hand. How big is the reaction force associated with the weight of the ball? What object is responsible for that force? How big is the force that the ball exerts on the hand? How big is the reaction force associated with this force? Now let the hand exert a 15 N force on the ball. How big is the reaction force associated with the weight of the ball? What object is responsible for that force? How big is the force that the ball exerts on the hand? How big is the reaction force associated with this force? 2b. A locomotive pulls a series of cars. Which is the correct analysis of the situation? a.) The train moves forward because the locomotive pulls forward slightly harder on the wagons than the wagons pull backward on the locomotive. b.) Because action always equals reaction, the locomotive cannot pull the cars--the cars pull backward just as hard as the locomotive pulls forward, so there is no motion. c.) The locomotive gets the cars to move by giving them a tug during which the force on the cars is momentarily greater than the force exerted by the cars on the locomotive. d.) The locomotive's force on the cars is as strong as the force of the cars on the locomotive, but the frictional force on the locomotive is forward and large while the backward frictional force on the cars is small. e.) The locomotive can pull the cars forward only if it weighs more than the cars. 2c. Are there any thoughts you wish to share, whether they are about this assignment, the reading (what seems impossible, what makes no sense, what you'd like to spend time on in class, what you really found interesting etc) or the course? |