Question

1. Emily takes her little brother Jake to the playground. Jake weighs 80 lbs = 400 N and Emily weighs 120 lbs = 600 N. Jake wants to play on the seesaw and sits at one end 3 m from the center. How far from the center should Emily sit to balance the seesaw?

2. Why does the Sun exert a larger gravitational force on you at noon today that at midnight tonight?

3. A solid cylinder and a hoop have the same mass and diameter. (a) Which one has a larger rotational inertia? Explain why. (b) If they are released simultaneously on an inclined board, which will reach the bottom first?

4. One friend says that when the space shuttle is in orbit, the astronauts float because there is no gravitational force on them. A second friend says he learned in physics class that the gravitational pull on the astronauts is more than 90 % of their weight while they are in orbit. What is the real reason the astronauts float in the shuttle?

5.A 50 g mass is hung from the 10 cm mark on a meter stick. It is found that the meter stick balances at the 40 cm mark. What is the mass of the meter stick? Hint: Draw a picture.

Answer 1

Solution) (1) Mj = 400 N

Me = 600 N

rj = 3 m

re = ?

To balance Torques must be equal

Tj = Te

T = r×F

Tj = Te

rj×Mj = re×Me

3×400 = (re)(600)

re = (3×400)/(600)

re = 2 m

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