Answer:
v=2.42m/s
Explanation:
We use the energy conservation theorem in order to solve the problem. The energy when the spring is compressed is equal at the energy when the disk leaves the spring:

At the beginning the initial energy is totally potential, energy linked to the compressed spring. At the end the energy is totally kinetics
We solve the equation in order to find the speed.
k=162 N/m
x=7 cm=0.07m
m=0.135 kg

Ke= 1/2 x m x v^2
Ke= 1/2 x 2.1 x 30^2
Energy = 945 J
Mu = 8.66 × 10^25 kg
Explanation:
centripetal force = gravitational force

where
m = mass of moon Ariel
mu = mass of Uranus
r = radius of Ariel's orbit
v = Ariel's velocity around Uranus
To find the velocity, we need to find the circumference of the no orbit and then divide it by the period (2.52 days):
circumference = 2πr = 2π×(1.91 × 10^8 m)
= 1.2 × 10^9 m
period = 2.52 days × (24 h/1 day)×(3600 s/1 hr)
= 2.18 × 10^5 s
v = (1.2 × 10^9 m)/(2.18 × 10^5 s)
= 5.5 × 10^3 m/s
(5.5 × 10^3 m/s)^2/(1.91 × 10^8 m) = (6.67 × 10^-11 m^3/kg-s^2)Mu/(1.91 × 10^8 m)^2
Solving Mu,
Mu = 8.66 × 10^25 kg