Problem 89
A schoolyard teeter-totter with a total length of \(5.2 \mathrm{~m}\) and a mass of \(38 \mathrm{~kg}\) is pivoted at its center. A 19-kg child sits on one end of the teeter-totter. Where should a parent push vertically downward with a force of \(210 \mathrm{~N}\) in order to hold the teeter-totter level?
Problem 91
Think \& Calculate A meterstick balances at its center. If an 86-g necklace is suspended from one end of the meterstick, the balance point moves \(8.2 \mathrm{~cm}\) toward that end. (a) Is the mass of the meterstick greater than, less than, or equal to the mass of the necklace? Explain. (b) Find the mass of the meterstick.
Problem 91
A meterstick balances at its center. If an \(86-g\) necklace is suspended from one end of the meterstick, the balance point moves \(8.2 \mathrm{~cm}\) toward that end. (a) Is the mass of the meterstick greater than, less than, or equal to the mass of the necklace? Explain. (b) Find the mass of the meterstick.
Problem 93
Dragonflies often dip into the water on the surface of a lake or pond, presumably to drink or to clean themselves. Recently, it has been discovered that after dipping the dragonflies fly straight upward, then pitch forward and tumble head over tail several times until the water has been shed from their bodies. Observations show that the dragonflies complete one revolution every \(0.017 \mathrm{~s}\) during this "spin dry" maneuver. What is their angular speed in radians per second and revolutions per minute? (For comparison, a typical car engine runs at about \(1500 \mathrm{rpm}\).)
Problem 95
Rotating Tray To provide uniform cooking microwave ovens have a glass tray that sits on top of a circular ring with three small wheels, as shown in Figure \(8.36\). When the tray rests on top of the wheels, it is rotated easily by a small motor in the base of the microwave. The rotation of the tray ensures even heating. When the tray completes one full revolution, how many revolutions has the circular ring underneath it completed? Explain.
Problem 97
Connect to the Big ldea How would you explain the difference between force and torque to a family member? Address the following questions: Can a force produce zero torque? Can a torque be produced without a force? Why is a force more effective in producing a torque when it is tangential than when it is radial?
Problem 97
How would you explain the difference between force and torque to a family member? Address the following questions: Can a force produce zero torque? Can a torque be produced without a force? Why is a force more effective in producing a torque when it is tangential than when it is radial?
