Right!

• The ball starts from rest (zero kinetic energy), and it's still moving when it goes through the goalposts, so its kinetic energy increases overall.
• The system includes both ball and the Earth, so it has gravitational potential energy, and this goes up as the ball rises.
• The external force acting on the system is the force of the kick, which does positive work.
• Lastly, for a closed system (which this is, if we neglect air resistance), the work done by the external force must equal the change in the system's energy.

Now answer this: if we chose the system to be only the ball, what would the work-energy diagram look like? Choose from the pictures shown below.

Click here to choose diagram (a).

Click here to choose diagram (b).

Click here to choose diagram (c).

Go back if you want to look at the original question.