No, we cannot touch gravity nor can we physically see it. We can only see how it works.
Answer:h=5.81 m
Explanation:
Given
Mass of block(m)=0.250 kg
Spring Constant 
Initial elongation =0.080 m=8 cm
Thus Initial Potential Energy stored =Final Potential Energy stored in Block






1) The heat added to system
2) 800J
3) I'm not sure but I think it would be 300J.. Not certain tho