Wanda exerts a constant tension force of 12 n on an essentially massless string to keep a tennis ball (m=60g) attached to the end of the string traveling in uniform circular motion above her head at a constant speed of 9.0 m/s. what is the length of the string between her hand and the tennis ball? you may ignore gravity in this problem (assume the motion of the tennis ball and string happen in a purely horizontal plane). a. 22 m
b. 2.5 m
c. 2.2 cm
d. 10 m

L = 40.5 cm

Explanation:

Since ball is rotating in horizontal plane with uniform speed

so here net force due to tension on the ball is centripetal force on the ball which is required to rotate the ball in circular path

so here we know

so here we have

as we know

m = 60 g = 0.060 kg

T = 12 N

v = 9.0 m/s

now from above formula

now we have

so L = 40.5 cm

when a device is used in a circuit in which the voltage is 81 v, the current flowing through the device is 3 a. what is the resistance of the device?

a. 27 ω

b. 40.5 a

c. 243 ω

d. 243 a

the correct answer is a. 27