Answer:
The tension on the string is
Explanation:
From the question we are told that
The mass of the rock is 
The density of the rock is
Generally the volume of the rock is mathematically evaluated as

substituting values


The volume of the rock immersed in water is
substituting values


mass of water been displaced by the this volume is
According to Archimedes principle
=> 

The weight of the water displace is



The actual weight of the rock is

The tension on the string is
substituting values
It's average speed during that 26 seconds was about 4.77 m/s. Without seeing the graph, we can't tell if it was going faster or slower at any particular time during that period. All we can tell is its average for the full interval.
We can use renewable sources
How many atoms are in something determines it "mass"