Substance A has a density of 3 g/cm3 and substance B has a density of 4 g/cm3. In order to obtain equal masses of these two substances, the ratio of the volume of A to the volume of B will be equal to
A) 1 : 4
B) 4 : 3
C) 3 : 4
D) : 1
E) 1 : 3
B
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An unfueled 1000-kg experimental rocket sled at rest on level frictionless rails is loaded with 50 kg of propellant. It exhausts the propellant in a 20 s "burn.". The rocket moves at 160 m/s after the burn. What average force is experienced by the rocket during the burn?
a. 0.80 × 10^4 N b. 0.75 × 10^4 N c. 0.60 × 10^4 N d. 0.35 × 10^4 N
Power is defined as the _________________ is done.
A) Amount of work which B) Angle at which C) Direction at which work D) The rate at which work.
An object is attached to a vertical spring and bobs up and down between points A and B. Where is the object located when the elastic potential energy of the system object-spring is a minimum?
A) at either A or B B) midway between A and B C) one-third of the way between A and B D) one-fourth of the way between A and B E) at none of the above points
A large 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on the one side is 28 W/(m2 K) and on the other side is 57 W/(m2 K). If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it will take for the copper plate to reach a temperature of 82°C.
GIVEN
• A large copper plate between two air streams whose temperatures suddenly change
• Plate thickness (2L) = 2.54 cm = 0.0254 m
• The heat transfer coefficients are
? lch = 28 W/(m2 K)
? 2ch = 57 W/(m2 K)
• Air temperature changes from 38°C to 93°C
FIND
• How long it will take for the copper plate to reach a temperature of 82°C
ASSUMPTIONS
• The initial temperature of the plate is 38°C
• The plate can be treated as an infinite slab
SKETCH
