Physics Chapters 1 2 3 Short Answer 1. Refer to the velocity-time graph. What is the instantaneous acceleration at t =4 s? Velocity v. Time 40 30 v (m/s [forward]) 20 10 - 0 - 0 2 t (s) 2. An object is moving such that its position-time graph and velocity-time graphs are both straight lines. The acceleration-time graph is a horizontal straight line. Formulate and present an argument why this should be the case. 3. A kitten walked 5.8 m [N] to eat some food, then an additional 4.2 m [W 40 S] to take a nap. Use the Sine and Cosine Laws to determine her total displacement. During a snowstorm an airplane is flying at 80.0 m/s and drops a bale of hay to a group of stranded cattle. The pilot plans to drop the bale of hay when he is directly over a barn that is 500.0 m from the cattle. What altitude should he adopt for the drop, in order to have the bale land at the location of the cattle? 5. A river flows from west to east at 1.50 m/s. A motorboat is aimed north across the river, and moves at 2.5 m/s relative to the water. The river is 100 m wide. How far downstream does the boat land 6. Three masses are suspended as shown. What is the tension in the string between the 1.20 kg mass and the 1.50 kg mass? 2.00 kg 1.2 kg 1.5 kg 7. A helicopter drops a cable which is attached to a load. The cable is partially reeled in, and the helicopter flies east. Air resistance causes the load to swing backwards such that it makes an angle of 20.0 with the vertical Draw a FBD of the situation.3. A student who has not studied physics claims that there is little danger from a large object if it is moving at a slow speed. For example, if a truck is moving at only one or two m/s, there is no danger if it hits you, since your body will only need to supply a small force to stop the truck. Reflect on what you have learning about forces and motion, and comment on this hypothesis. 9. Reflect on your knowledge of Newton's Third Law of Motion. Select an example that you have witnessed in your own life, and explain how it works. 10. A bird in a cage has a total mass of 18.0 kg, and is hanging in an elevator from a spring balance. The balances reads 225 N. Determine the state of motion of the elevator. 11. 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? 12. A starship in a science fiction movie was in free-fall far from any massive body. The captain had a mass of 80.0 kg and entered a turbolift that accelerated him toward the bridge at 3g. What was the apparent weight experienced by the captain 13. A Teflon wheel in an industrial machine has a radius of 2.54 cm. To prevent undue stretch of the Teflon material, the maximum centripetal acceleration at the edge of the wheel cannot exceed 20.0g. What is the maximum frequency of rotation permitted for the wheel? 14. 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? 15. A long-range artillery weapon can shoot projectiles up to 50.0 km. If the target is due north of the gun, the gun must be aimed to one side of the target in order to hit it. Explain why this is necessary in terms of rotating frames of reference