Homework #5

These are due on Friday October 8th in class.

This time I have split it into three parts. The first two parts are quite short and will go to the graders as usual. The third part consists of multiple choice questions that I will grade. They are slighly odd because I ask for a SHORT explanation for each. They are here to give you some practice with multiple choice physics questions because they are what you will find on the MCAT. I thank Gordon Jones for lending me some of these questions.

Part I

5Q9)

5Q13)

5P13)

5P19)

6.42)

Part II

5Q10)

6Q5)

5P39) (Please remember that force is a vector.)

6.20)

6.55)

Part III (Courtesy of Gordon Jones)

10) A boy attaches a string to a stone and whirls it round his head making 1 complete revolution every second. Under these conditions the tension in the string is FT. Now, if the boy speeds up the stone so that it make 2 revolutions per second, keeping the radius of the circle unchanged, what happens to the tension in the string?

A) Tension falls to one quarter of its previous value
B) Tension falls to one half of its previous value
C) Tension is unchanged
D) Tension increases to twice its previous value
E) Tension increases to four times its previous value

Briefly explain your reasoning.

12) A plane travelling at 200 m/s follows a path that is a vertical circle of radius R. At the top of the path, the passengers experience complete weightlessness. To 1 significant figure, what is the value of R?

A) 200 m B) 1000 m C) 2000 m D) 4000 m E) 40,000 m

Briefly explain your reasoning with a free body diagram.

13) A spaceship is in orbit abound the earth at an altitude of 12,000 miles. Its inhabitants experience weightlessness. Which of the following statements best explains why?

A) The centripetal force of the earth on the astronaut in orbit is zero.
B) The pull of the earth on the spaceship is cancelled by the pull of the other planets.
C) The spaceship is in free fall and its floor cannot press upward on the astronauts.
D) The force of gravity descreases as the inverse square of the distance from the centre of the earth.
E) The force of gravity does not reach that far from the earth.

Briefly explain your reasoning.

Physics 100