A world-class sprinter can reach a top speed (of about 11.5 m s) in the first 15.0 m of a race. What is the average acceleration of this sprinter and how long does it take her to reach that speed?
What will be an ideal response?
Ans:
4.41 m/s2
2.60 sec
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Consider a design for a nuclear reactor using natural-convection heating of liquid bismuth as shown. The reactor is to be constructed of parallel vertical plates 1.8 m tall and 1.2 m wide, in which heat is generated uniformly. Estimate the maximum possible heat dissipation rate from each plate if the average surface temperature of the plate is not to exceed 870°C and the lowest allowable bismuth temperature is 315°C.
GIVEN
• Vertical plates with uniform heat generation in bismuth
• Plate height (L) = 1.8 m
• Plate width (w) = 1.2 m
• Maximum average surface temperature (Ts) = 870°C
• Minimum bismuth temperature (T?) = 315°C
FIND
• Maximum possible heat dissipation rate (q) from each plate
ASSUMPTIONS
• Steady state
• Free convection only
• Edge effects are negligible
SKETCH
PROPERTIES AND CONSTANTS
for bismuth at the mean temperature of (592.5°C)
Thermal conductivity (k) = 15.58 W/(m K)
Kinematic viscosity (?) = 0.991 × 10–7 m2/s
Prandtl number (Pr) = 0.010 Also Density at 538°C (?538) = 9739 kg/m3 Density at 649°C (?649) = 9611 kg/m3
To find the thermal expansion coefficient (?)
Work Done by a Gas: A gas expands from an initial volume of 0.040 m3 to a final volume of 0.085 m3 while its pressure increases linearly with the volume (so that the process follows a straight-line path in a pV diagram) from 110 kPa to 225 kPa. How much work is done by the gas during this expansion?
A. 5.2 kJ B. 7.5 kJ C. 7.8 kJ D. 11 kJ E. 12 kJ
An electron (charge ?1.6 × 10^?19 C) moves on a path perpendicular to the direction of a uniform electric field of strength 2.0 N/C. How much work is done on the electron as it moves 14.0 cm?
a. 5.6E–19 J b. ?2.8E–19 J c. 1.6E–19 J d. 3.9E–18 J e. zero
The angular diameters of the Moon and Sun vary slightly because the orbits of the Moon and Earth are slightly elliptical
a. True b. False Indicate whether the statement is true or false