What is SI unit of speed​

m/s

Explanation:

The SI unit of speed is the metre per second, but the most common unit of speed in everyday usage is the kilometre per hour or, in the US and the UK, miles per hour.

m/s

which is also written as

ms-¹

The above mentioned symbols are said as 'meter per second'

hope it helps!

the one with the highest speed

the chart show the masses and velocities of two colliding objects that stick together after a collision.

according to the law of conservation of momentum, the momentum of the object after the collision is  

answer

1,500

kg • m/s.