Newton's Second Law in 2 Dimensions: A 40-kg box is being pushed along a horizontal smooth surface. The pushing force is 15 N directed at an angle of 15° below the horizontal. What is the magnitude of the acceleration of the crate?
A. 0.16 m/s2
B. 0.36 m/s2
C. 0.47 m/s2
D. 0.39 m/s2
E. 0.68 m/s2
Answer: B
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Heat transfer from an electronic circuit board is to be determined by placing a model for the board in a wind tunnel. The model is a 15-cm-square plate with embedded electrical heaters. The wind from the tunnel air is delivered at 20°C. Determine the average temperature of the model as a function of power dissipation for an air velocity of 2.5 and 10 m/s. The model is pitched 30° and yawed 10° with respect to the flow direction. The surface of the model acts as a blackbody.
GIVEN
• A Model square electronic circuit board pitched 30° and yawed 10° in a wind tunnel
• Length of a side (L) = 15 cm = 0.15 m
• Air temperature (T?) = 20°C = 293 K
• Air velocity (U?) = 2.5 m/s or 10 m/s FIND
• The average surface temperature of the model (Ts) as a function of power dissipation (Q )
ASSUMPTIONS
Steady state
The surface of the model acts as a black body (? = 1.0)
The wind tunnel acts as a black body enclosure at the air temperature.
SKETCH
Astronomical alignments in antiquity on solstice and equinox sunrises and sunsets show us these builders had developed a ________ for farming
Fill in the blank(s) with correct word
A flute behaves like a tube open at both ends. If its length is 67.0 cm, and the speed of sound is 340 m/s, what is its fundamental frequency in Hz?
a. 127 Hz b. 168 Hz c. 670 Hz d. 254 Hz e. 507 Hz
The circuit below contains 5 identical light bulbs. The emf is 110 V. Which light bulb(s) is(are) brightest?
a.
A: The one closest to the positive terminal of the battery.
b.
A and C: The bulbs closest to the positive terminal of the battery.
c.
A and B: Because they are closest to the terminals of the battery.
d.
C and D: Because they receive current from A and B and from E.
e.
E: Because the potential difference across E is that of the battery.