When a cannonball is fired from a cannon, which undergoes the greater acceleration?
A) the cannonball
B) the recoiling cannon
C) both the same
Answer: A
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Which is the strongest of the fundamental forces in the universe?
A) strong force B) weak force C) electromagnetic force D) gravitational force E) All four forces have the same strength.
Express the result of the following calculation, to the proper number of significant figures: 50.19 – 7966 × 10-3
What will be an ideal response?
Explain radiation darkening
What will be an ideal response?
A stainless steel cylindrical billet [k = 14.4 W/(m K), ? = 3.9 × 10–6 m2/s] is heated to 593°C preparatory to a forming process. If the minimum temperature permissible for forming is 482°C, how long can the billet be exposed to air at 38°C if the average heat transfer coefficient is 85 W/(m2 K)? The shape of the billet is shown in the sketch.
GIVEN
• A stainless steel cylindrical billet exposed to air
• Thermal conductivity (k) = 14.4 W/(m K)
• Thermal diffusivity (?) = 3.9 × 10–6 m2/s
• Initial temperature (To) = 593°C
• The minimum temperature permissible for forming is 482°C
• Air temperature (T?) = 38°C
• Average heat transfer coefficient ( )ch = 85 W/(m2 K)
FIND
• How long may the billet be exposed to the air?
ASSUMPTIONS
• End effects are negligible
• Constant heat transfer coefficient
• Conduction in the radial direction only
• Uniform thermal properties
SKETCH
