Wood from an ancient stump has a ratio of carbon-14 to carbon-12 that is one-eighth that of new wood. About how old is the stump? (Carbon-14's half-life is 5730 years.)
17,190 years
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Mass on a Spring: A 0.150-kg air track cart is attached to an ideal spring with a force constant (spring constant) of 3.58 N/m and undergoes simple harmonic oscillations. What is the period of the oscillations?
A. 2.57 s B. 0.527 s C. 0.263 s D. 1.14 s E. 1.29 s
The heat transfer coefficients for the flow of 26.6°C air over a 1.25 cm diameter sphere are measured by observing the temperature-time history of a copper ball of the same dimension. The temperature of the copper ball (c = 376 J/(kg K), ? = 8928 kg/m3) was measured by two thermocouples, one located in the center, and the other near the surface. The two thermocouples registered, within the accuracy of the recording instruments, the same temperature at any given instant. In one test run, the initial temperature of the ball was 66°C and the temperature decreased by 7°C in 1.15 min. Calculate the heat transfer coefficient for this case.
IVEN
• A copper ball with air flowing over it
• Ball diameter (D) = 1.25 cm = 0.0125 m
• Air temperature (T?) = 26.6°C
• Specific heat of ball (c) = 376 J/(kg K)
• Density of the ball (P) = 8928 kg/m3
• Thermocouples in the center and the surface registered the same temperature
• Initial temperature of the ball (To) = 66°C
• Lapse time = 1.15 min = 69 s
• The temperature decrease (To – Tf) = 7°C
FIND
• The heat transfer coefficient ch
ASSUMPTIONS
• The heat transfer coefficient remains constant during the cooling period.
SKETCH
A speed boat requires 85.0 kW to move at a constant speed of 14.0 m/s. What is the resistive force of the water at this speed?
a. 1 190 N b. 6 070 N c. 6 170 N d. 5 970 N e. 1 290 N
A rectangular loop (area = 0.15 m2) turns in a uniform magnetic field with B = 0.20 T. At an instant when the angle between the magnetic field and the normal to the plane of the loop is (?/2) rad and increasing at the rate of 0.60 rad/s, what is the magnitude of the emf induced in the loop?
A. 24 mV B. zero C. 18 mV D. 20 mV E. 6.0 mV