Awire of length l and cross-sectional area a has resistance r what will be the resistance of the wire if it is streched to 3 times its original legnth?

9R or R'=9pL1/A1 or the resistance has increased 9 times the original resistance

Explanation:

When we then to enlongate a wire such that the area of the wire diminshes so As to have a constant volume.

From the relation

R=pL1/A1

Where p=resistivity

L1=original length

R=resistance

A1=original area

L2=3L1.since the volume remain constant

A1L1=A2L2

A2=A1L1/3L1

A2=A1/3

Since the resistance and resistivity of the wire does not change before strecting and after stretching

L1= 3L1

A2=(A1/3)

R'=pL2/A2

R'=p 3L1/ (A1/3)

R'=p9L1/A1

R'=9pL1/A1

R=pL1/A1

So the resistance has increased 9 times the original resistance

total distance travelled = 60 miles

total time taken =1.5 hours

average speed = total distance / total time

60 / 1.5

= 40

therefore, average speed = 40 m/h

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