A bullet is fired through a board, 14.0 cm thick, with its line of motion perpendicular to the face of the board. If it enters with a speed of 450 m/s and emerges with a speed of 220 m/s, what is the bullet's acceleration as it passes through the board?
A. ?500 km/s2
B. ?550 km/s2
C. ?360 km/s2
D. ?520 km/s2
E. ?275 km/s2
Answer: B
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A wire of perimeter P and cross-sectional area A emerges from a die at a temperature T (above ambient temperature) and with a velocity U. Determine the temperature distribution along the wire in the steady state if the exposed length downstream from the die is quite long. State clearly and try to justify all assumptions.
GIVEN
• A wire emerging from a die at a temperature (T) above ambient
• Wire perimeter = P
• Cross-sectional area = A
• Wire emerges at a temperature T above ambient
• Wire velocity = U
FIND
• The temperature distribution along the wire in the steady state if the exposed length downstream from the die is quite long. State clearly and try to justify all assumptions
ASSUMPTIONS
• Ambient temperature is constant at T?
• Heat transfer coefficient between the wire and the air is uniform and constant at hc
• The material properties of the wire are constant
? Thermal conductivity = k
? Thermal diffusivity = ?
• Axial conduction only
• Wire temperature is uniform at a cross section (negligible internal thermal resistance)
SKETCH
