When the wheels of the skateboard get stuck in the crack of the sidewalk, the riders inertia will continue forward and cause him to fall off/down.
A parachute is a device used to slow down an object that is falling towards the ground. without a parachute the gravity is more than air resistance. But, as the parachute opens, the air resistance increases.
hope this was useful
We have: K.E. = mv² / 2
Here, m = 1 Kg
v = 4 m/s
Substitute their values in the formula,
K.E. = 1×4² / 2
K.E. = 16/ 2
K.E. = 8 J
Finally, answer of your question would be 8 Joules.
Hope this helps!