A child sits on a swing supported by ropes of length 4.0 m. With what frequency will she need to apply the driving force to maintain swinging?
a. 0.29 Hz
c. 0.25 Hz
b. 0.48 Hz
d. 0.38 Hz
C
You might also like to view...
Which of the following statements is true of stars?
A) Stars should have very low densities to support their own weight. B) Stars should have very low temperatures to support their own weight. C) The pressure of a gas near the surface of a star does not need to be high for stability. D) The temperature of a gas near the center of a star does not need to be high for stability.
Derive an equation of the form hc = f(T, D, U) for turbulent flow of water through a long tube in the temperature range between 20° and 100°C.
GIVEN
• Turbulent water flow through a long tube
• Water temperature range (Tb) = 20°C to 100°C FIND
• An expression of the form h c= f(T, D, U)
ASSUMPTIONS
• Steady state
• Variation of properties with temperature can be approximated with a power law
• Fully developed flow
• Water is being heated
SKETCH
PROPERTIES AND CONSTANTS
for water
When steam condenses, the H2O
1) releases energy. 2) absorbs energy. 3) neither of these. When water freezes, the H2O 4) releases energy. 5) absorbs energy. 6) neither of these.
A common 5-liter metal can will float in air if it is
A) evacuated of air. B) filled with a very large amount of helium. C) thrown high enough. D) no way, unless the displaced air weighs more than the can and its contents!