Answer:
Change in potential energy = 7350 Joules
Explanation:
It is given that,
Side of cube, a = 0.5 m
Density of cube, 
The cube is lifted vertically by a crane to a height of 3 m
We know that, density 
So, m = d × V (V = volume of cube = a³)

m = 250 kg
We have to find the change in potential energy of the cube. At ground level, the potential energy is equal to 0.
Potential energy at height h is given by :

PE = 250 kg × 9.8 m/s² ×3 m
PE = 7350 Joules
So, change in potential energy of the cube is 7350 Joules.
During an exothermic reaction; light and heat are released into the environment.
An exothermic reaction is one in which heat is released to the environment. This heat can be physically observed sometimes like in an a combustion reaction.
In an exothermic reaction, the enthalpy of the reactants is greater than the enthalpy of the products.
This heat lost is sometimes felt as the hotness of the vessel in which the reaction has taken place.
In conclusion, light and heat are released into the environment in an exothermic reaction.
Learn more: brainly.com/question/4345448
V=at and a=F/m
140/.070 = 2000m/s^2
2000*.020 = 40m/s
The ball’s velocity increased by 40m/s.