7. what is the kinetic energy of a 3-kilogram ball that is rolling at 2 meters per second?
8. two objects were lifted by a machine. one object had a mass of 2 kilograms, and was lifted at a speed of
2 m/sec. the other had a mass of 4 kilograms and was lifted at a rate of 3 m/sec.
a. which object had more kinetic energy while it was being lifted?
b. which object had more potential energy when it was lifted to a distance of 10 meters? show your
calculation.

Kinetic energy = 0.5*M*V^2 

 Q7-
 
0.5*3*(2^2)= 6J

Q8a- 

0.5*2*(2^2)= 4J
0.5*4*(3^2)=18J 
the second ball has more kinetic energy.

Q8b-

at the max height, all the kinetic energy is converted to potential energy, 

gravitational potential energy is = M*g*h

that theory would apply if you wanted to work out the maximum height achieved if the balls were thrown upward by rearranging. But, we are simply working out which ball will have more potential energy so:

First ball:
2kg*9.81(g)*10m = 196.2J

Second ball
4kg*9.81*10m= 392.4J

The second ball has more potential energy