The magnitude j of the current density in a certain wire with a circular cross section of radius r = 2.11 mm is given by j = (3.25 × 108)r2, with j in amperes per square meter and radial distance r in meters. what is the current through the outer section bounded by r = 0.921r and r = r?

Explanation:

As we know that current density is ratio of current and area of the crossection

now we have

so the current through the wire is given as

now we have

here we have

now plug in the values in above equation

now we have

now plug in both limits as mentioned

here R = 2.11 mm

i think the answer would be b

when jerome paddle in flowing river towards east the net speed of jerome will increase

so the net speed of jerome will be given as

now the speed of paul will be same as it is given as he is running on the ground

so

so here we can say since the speed of jerome is more so he will win the race

now as we know the distance so the time difference is given as

so jerome will reach first and the time difference will be 203.55 s or 3.4 min