Chapter 1 2 3 SPH4U Short Answer 1. Consider what you have learned about the concepts of average speed and average velocity. Select an example from your own experience that illustrates the difference in meaning of these concepts. 2. While riding in his father's car, Anselmo noticed that the speedometer of the car read 75 km/h. He looked out the side window for 10 s, and then back at the speedometer, which read 50 km/h. Anselmo calculated that the vector acceleration of the car must have been about 2.5 km/h/s [forward]. Is he correct? Explain your answer. 3 . A river flows north at 1.2 m/s. Sandor puts his kayak in the water and paddles north at a speed of 1.4 m/s relative to the water. At the same time and place, Elisa puts her kayak in the water and paddles south at 1.6 m/s relative to the water. After 2.0 hours, both paddlers turn around and continue to paddle with the same speeds relative to the water until they meet. They predict that will meet again after an additional 2.0 h. Are they correct? Explain your answer. 4. Newton's First Law of Motion says that no net force is needed for a moving object to continue moving in a straight line at a constant speed. In real life, you may have noticed that something like a moving soccer ball will eventually come to a stop, even if no one exerts a force on it. How would you explain this discrepancy to a friend who has not studied physics? 5. You can pull on a rope with a maximum force of 2.00 % 10 N. You have been challenged to a tugging contest by an opponent who can pull with a force of 2.80 * 10 N. You are allowed to use one pulley and one fixed support such as soccer goalpost. You set up the situation as shown. What is the maximum angle & you can use that will still let you at least draw the contest? You A Tree Pulley Opponent 6. Reflect on the concepts and examples you learned about in this chapter. Select one that was surprising to you, and explain why it changed your views 7. Hosni pushes on a box with a force of 45.0 N directed at 21.0 below the horizontal. He fails to move the box. The coefficient of static friction between the box and the floor is 0.724. What is the smallest possible value for the mass of the box? 8. A passenger standing in an elevator feels an apparent weight three times normal. Determine the state of motion of the elevator. Explain your answer.. At the end of a free-fall ride, the brakes kick in and decelerate the riders at 4g. What is the apparent weight of a 75.0 kg rider during braking? 10. A hockey puck is placed on the floor of a bus. The coefficient of static friction between the puck and the floor is 0.654. What is the minimum acceleration required for the bus before the puck begins to slide relative to the floor? 11. Teenagers of the 1950s enjoyed playing their favourite songs on records that turned at 78.0 rpm on a turntable with a diameter of 25.4 cm. The record was played with a needle that had a mass of 36.8 g. What was the minimum centripetal force needed to keep the playing needle in the groove at the outer edge of the record? 12. A ride at an amusement park consists of a rotating cylinder with a radius of 5.00 m. After it reaches a certain speed, the floor drops away, and riders are held to the walls via the force of static friction. The coefficient of static friction between a rider and the wall is 0.400. What is the minimum speed needed to ensure that the rider will not slide down the wall? 13. Reflect on your learning. How has learning about uniform circular motion changed the way you think about things that are part of your everyday life? 14. A planet has a radius of 4.00 10 m, and rotates so rapidly that an object on the equator feels only 10% of the weight that it feels at the poles. What is the speed of an object at the equator? 15. Is it fair to compare current results to those of previous sporting events