PHYSICS MIDDLE SCHOOL

Which of the following has the lowest U value?a. plywood
b. poured concrete
c. expanded polyurethane
d. asbestos shingles

Answers

Answer 1
Answer:

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

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Answers

Answer:

A is the correct answer

Explanation:

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5. Kelvin applied a rightward force of 302 N to a 29 kg desk to accelerate it across the floor. Thecoefficient of friction between the desk and the floor is 0.750.
a. Calculate the Force Friction
FN

Answers

The force of friction is 213.2 N

Explanation:

The frictional force acting on an object sliding on a surface is given by:

F_f = \mu mg

where:

\mu is the coefficient of friction

m is the mass of the object

g is the acceleration of gravity

In this problem we have

\mu=0.750

m = 29 kg

g=9.8 m/s^2

Therefore, the force of friction is

F_f = (0.750)(29)(9.8)=213.2 N

Learn more about friction:

brainly.com/question/6217246

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#LearnwithBrainly

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Answers

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A train travels 98 kilometers in 1 hours, and then 78 kilometers in 3 hours. what is its average speed?this is a fill in the blank question. thanks!

Answers

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