1. Forces, Uniform Circular Motion, and Gravity Review October 7

2. A force F acts on mass m 1 giving acceleration a 1. The same force acts on a different mass m 2 giving acceleration a 2 = 2a 1. What is the acceleration if the same force pushes on both blocks? 0 0 47 60 F a1a1 m1m1 F a 2 = 2a 1 m2m2 F m2m2 m1m1 a3a3 1.4/3 a 1 2.3/2 a 1 3.1/2 a 1 4.3/4 a 1 5.2/3 a 1

3. Astronauts can not weigh themselves on a conventional scale (no normal force is produced). Discuss with your neighbor ways of measuring the mass of an astronaut while in space. 99 1.. 2..

4. When you climb up a rope, the first thing you do is pull down on the rope. How do you manage to go up the rope by doing that? 0 0 47 60 1.this slows your initial velocity which is already upward 2.you don’t go up, you’re too heavy 3. you’re not really pulling down -- it just seems that way 4.the rope actually pulls you up 5.you are pulling the ceiling down

5. If you push with force F on either the heavy box (m 1 ) or the light box (m 2 ), in which of the two cases below is the contact force between the two boxes larger? 0 0 47 60 F m2m2m2m2 m1m1m1m1A F m2m2m2m2 m1m1m1m1B 1.Case A 2.Case B 3.Same in both cases

6. Three blocks of mass 3m, 2m, and m are connected by strings and pulled with constant acceleration a. What is the relationship between the tension in each of the strings? 0 0 47 60 T3T3 T2T2 T1T1 3m 2m m a 1.T 1 > T 2 > T 3 2.T 1 < T 2 < T 3 3.T 1 = T 2 = T 3 4.all tensions are zero 5.tensions are random

7. A box sits on a flat board. You lift one end of the board, making an angle with the floor. As you increase the angle, the box will eventually begin to slide down. Why? 0 0 47 60 Net Force Normal Weight 1.The component of the gravity force parallel to the plane increased 2.coeff. of static friction decreased 3.normal force exerted by the board decreased 4.both #1 and #3 5.all of #1, #2 and #3

8. A ping pong ball is shot into a circular tube which is lying flat (horizontal) on a tabletop. When the ping pong ball leaves the track, which path will it follow? 60 0 0 47 1.1 2.2 3.3 4.4 5.5

9. A rider in a “barrel of fun” finds herself stuck with her back to the wall. Which diagram correctly shows the forces acting on her? 0 0 47 1 2 3 4 5 1.1 2.2 3.3 4.4 5.5 60

10. You swing a ball at the end of string in a vertical circle. Since the ball is in circular motion there has to be a centripetal force. At the top of the ball’s path, what is F c equal to? 0 0 47 60 R v top 1.F c =F T - mg 2.F c =F T + F N - mg 3.F c =F T + mg 4.F c =F T 5.F c =mg

11. A planet of mass m is a distance d from Earth. Another planet of mass 2m is a distance 2d from Earth. Which force vector best represents the direction of the total gravitation force on Earth? 0 0 47 60 1.1 2.2 3.3 4.4 5.5 1 2 3 4 5 2d d 2m m Earth

12. Answers 1.5 – 2/3 a since m1+m2=3/2m1 2.Apply known force and measure acceleration (this assumes inertial mass = gravitational mass, which is now experimental fact) 3.4 4.1 – Case A – Fcontact must push a larger mass for same acceleration 5.1 6.4 – 1 and 3 7.2 8.1 – mg, friction, normal 9.3 – if velocity is just right so mv^2/R=mg, then tension=0 and momentarily in freefall 10.2 – gravity is directly proportional to m and inversely proportional to R^2, so bigger planet farther away in this case has ½ the gravitational force, so does not add an equal component to total force as the smaller, closer planet