Answer:
619.8 N
Explanation:
The tension in the string provides the centripetal force that keeps the rock in circular motion, so we can write:

where
T is the tension
m is the mass of the rock
v is the speed
r is the radius of the circular path
At the beginning,
T = 50.4 N
v = 21.1 m/s
r = 2.51 m
So we can use the equation to find the mass of the rock:

Later, the radius of the string is decreased to
r' = 1.22 m
While the speed is increased to
v' = 51.6 m/s
Substituting these new data into the equation, we find the tension at which the string breaks:

The work done by the three students is 3,000 J.
The energy transferred in the process is 3,000 J.
<h3>What is work done?</h3>
- Work done is the product of force and distance moved by the object.
W = Fd
The work done by the three students is calculated as follows;
W = 300 x 10
W = 3,000 J
<h3>What is energy transfer?</h3>
- This is means by which energy is converted from one form to another.
The energy transferred in the process is determined by work energy theorem.
E = W
E = 3,000 J
Learn more about work-energy theorem here: brainly.com/question/22236101
The end or finish of an event or process.