Answer:
23 km/h
Explanation:
Let's take the direction "towards Lilah" as positive direction.
Then, we can write Felipe's velocity with respect to Lilah as
At the same time, Felipe throws the football forwards, towards Lilah. The velocity of the ball with respect to Felipe (and the skateboard) is
Since both Felipe and the ball are moving in the same direction, then the velocity of the ball with respect to Lilah can be calculated by adding the two velocities:
The mass of the sheet of aluminium is the product between its density d and its volume V:
Re-arranging the equation, we can find the volume of the sheet:
Converted in millimeters,
The area is
Since
, this area corresponds to
So we can now find the thickness of the sheet of aluminium: