Answer:
c. expanded polyurethane
Explanation:
Thermal performance of a building fabric is measured in terms of heat loss and is expressed as U-value or R-value. U-value is the rate of heat transferred through a structure divided by the difference in temperature across the structure with a unit of measurement of W/m²K.You can calculate the U-value of a by getting the reciprocal of the sum of thermal resistances , R, making the building material.
If you have the value of R, then U=1/R
Material size R U
plywood 1" 1.25 0.8
Poured concrete 2" 0.99 1.010
Expanded polyurethane 1" 6.5 0.1538
Asbestos shingles 1" 0.03 33.33
The material with lowest U-value is expanded polyurethane
Answer:
Average power output of insect is 2.42W
Explanation:
Workdone by constant force during displacement is given by:
W= F× d cos theta
Where theta is angle between F and d.
Power output due to the force over the interval time is given by:
P= Workdone/change in time
Ginen:
Mass of insect,m= 7.0g= 7/1000 = 0.07kg
Downward force applied by insect,F= 2mg
Distance moved by the wing each stroke=1.5cm=1.5/100= 0.015m
W= F× d cos theta
Where theta=0° since force is in the same direction as the displacement.
W= 2mg×d
W= 2× 0.07 × 9.8 × 0.015
W= 0.02058J
Power output = W/ change in time
Since wings make 117strokes each second time interval is 1/117 = 8.5×10^-3seconds
Power= 0.02058/(8.5×10^-3)
Power= 2.42W
Answer:
F_aplied = fr
Explanation:
Newton's second law states that the force is proportional to the acceleration of the system, as in this case they indicate that the body moves at constant speed, the acceleration is zero, therefore
F_applied - fr = 0
F_aplied = fr
therefore the force applied by people is equal to the friction force
