Answer:
His impact velocity is 7 m/s.
Step-by-step explanation:
A stunt performer falls off a wall that is 2.5 m high and then lands on a mat. Let v is his impact velocity.
Concept used : Law of conservation of energy
Using the law of conservation of energy of the person such that,

g is acceleration due to gravity, g = 9.8 m/s²

So, his impact velocity is 7 m/s.