Answer:
0.423m
Explanation:
Conversion to metric unit
d = 4.8 cm = 0.048m
Let water density be 
Let gravitational acceleration g = 9.8 m/s2
Let x (m) be the length that the spring is stretched in equilibrium, x is also the length of the cylinder that is submerged in water since originally at a non-stretching position, the cylinder barely touches the water surface.
Now that the system is in equilibrium, the spring force and buoyancy force must equal to the gravity force of the cylinder. We have the following force equation:
Where 
N is the spring force, 
is the buoyancy force, which equals to the weight 
of the water displaced by the submerged portion of the cylinder, which is the product of water density 
, submerged volume 
and gravitational constant g. W = mg is the weight of the metal cylinder.
The submerged volume would be the product of cross-section area and the submerged length x
Plug that into our force equation and we have
Efficiency = Power Output / Power Input
Power Input = Rate of Energy input = 44.4 MJ/kg * 5 kg/h
= 222 MJ/h
But 1 hour = 3600seconds
222 MJ/h = 222 MJ/3600s = 0.061667 MW J/s = Watts
Power input = 0.061667 MW = 61 667 W
From Efficiency = Power Output / Power Input
28% = Power Output / 61667
Power Output = 0.28 * 61667
Power Output = 17266.76 W
Power Output ≈ 17 267 W
Rate of heat rejection = Power Input - Power Output
= 61667 - 17267 = 44400 W
Rate of heat rejection = 44 400W.
Answer:
B) Blackbody radiation
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Explanation:
The small mass of lens in a DVD player accounts for small inertia of the lens. Hence, even on application of force of small magnitude, the lens is rapidly accelerated. Moreover, the small mass of lens also accounts for lower resistance to change in its motion and therefore, again can be rapidly accelerated back and forth.
