Tom Hubsch
Physics
10/1/13

8. When a car moves along the highway at a constant velocity, the net force on it is zero. Why, then, do you continue running your engine? The engine continues to run because there is force working against the vehicle. The tires rolling along the pavement create friction, as well as wind resistance hitting your windshield, create a force that can only be counteracted by the engine creating an equal or greater opposing foce.

17. You hold an apple over your head. a. Identify all the forces acting on the apple and their reaction forces.
b. When you drop the apple, identify all the forces acting on it as it falls and the corresponding reaction forces.
A. My arm is a force holding the apple in the air, and gravity is pulling the apple downward.
B. When I drop the apple, my arm is no longer a factor, but gravity still pulls the apple downward toward the Earth.
25. Suppose the two carts, one twice as massive as the other, fly apart when the compressed spring that joins them is released. How fast does the heavier cart roll compared with the lighter cart? Newton’s Second Law states that Force=mass times acceleration. So to find acceleration, you will divide force by mass. This means that the heavier cart will have half of the acceleration as the lighter cart.
33. Why is it that a cat that falls from the top of a 50-story building will hit a safety net below no faster than if it fell from the 20th story? As the cat falls, it begins to accelerate due to gravity. Wind resistance acts as an upward force and increases as acceleration increases. Eventually, the force upward will equal the weight of the cat and it will then reach a constant speed. This is also known as terminal velocity.
43. A stone is shown at rest on the ground. a. The vector shows the weight of the stone. Complete the vector diagram showing another vector that