# Unit 2 Extra Credit

1. Consider two identical cans, one filled with lead and the other empty. The cans are located far in space at a place where they are "weightless". Describe a method of determining which can has the greater mass.

2. Why is it more difficult to push a stalled car from a position of rest than it is to keep it in motion once it is rolling?

3. Consider hitting a baseball with a bat. If we call the force of the bat against the ball the action force, identify the reaction force.

4. Each of the chain of bones forming your spine is separated from its neighbors by disks of elastic tissue. What happens, then, when you jump heavily on your feet from an elevated position? Can you think of a reason why you are a little taller in the morning than at night?

5. An empty hand is not hurt when it bangs lightly against a wall. Why is it hurt if it does so while carrying a heavy load?

6. A strongman is standing between two identical freight cars of equal mass. He pushes on both cars while his feet are off the ground. Is it possible for him to set either of the cars in greater motion than the other? Why or why not?

7. Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars?

8. What is meant by "free fall"? Why doesn't a heavy object fall faster than a lighter object when both are in a state of free fall?

9. In a tug-of-war, what is the net force acting on the rope when the participants each pull with opposing forces of 500 N? _________ What is the tensional force within the rope? ________

10. In terms of inertia, what is the disadvantage of a lightweight camera when snapping the shutter? Why is a massive tripod preferred by most photographers?

11. If we find a body that we know to be acted on by a force, but that is not moving, what inference can we draw about its state of motion?

12. Do you find it easier to walk on a carpeted floor than one having a polished smooth surface? Why?

13. Suppose two carts, one twice as massive as the other, fly apart when a compressed spring that is between them is released. How fast does the heavier cart roll compared to the lighter cart?

14. Two people of equal mass attempt a tug-of-war with a 12 meter rope while standing on frictionless ice. When they pull on the rope, they each slide toward each other. How do their accelerations compare, and how far does each person slide before meeting?

15. How does the weight of a falling body compare to the air resistance it encounters just before it reaches terminal velocity? ___________ After?___________ Explain both answers.

Resources for physics students are available through links on the GBS Physics Home Page. Such resources include the Multimedia Physics Studios (a collection of animations and movies which illustrate key physics concepts) and The Physics Classroom (an online tutorial written in an easy-to-understand language).