If r is the total resistance for a parallel circuit with two resistors of resistance r1 and r2, then . find the resistance, r1, if the total resistance r is 20 ohms, and r2 is 75 ohms. round your answer to the nearest ohm if necessary. 1/r = 1/r1+1/r2

Aball is thrown from the top of a building with an initial velocity of 21.9 m/s straight upward, at an initial height of 51.6 m above the ground. the ball just misses the edge of the roof on its way down, as shown in the figure. (a) determine the time needed for the ball to reach its maximum height. (b) determine the maximum height. (c) determine the time needed for the ball to return to the height from which it was thrown, and the velocity of the ball at that instant. (d) determine the time needed for the ball to reach the ground. (e) determine the velocity and position of the ball at t = 5.35 s.