Hello there!
The formula for momentum is
.
p is momentum, m is mass, and v is velocity.
The mass of a heavy moving van will be much greater than the mass of a motorcycle, so how can they have the same momentum?
They can have the same momentum if the velocity of the moving van is less than the velocity of the motorcycle, or if the velocity of the motorcycle is greater than the moving van (same thing but differently worded)
Let the mass of the moving van be greater than the mass of the motorcycle by a factor of k. In order for the two to have the same momentum, the velocity of the motorcycle must be greater than the velocity of the moving van by the same factor, k.
Hope this helps! :)