investigators are on the scene of a terrible traffic accident involving a large truck and a passenger van. the van had been stopped at a red light, but the large truck's brakes had failed so it plowed into the stationary van. how would they calculate the amount of momentum with which the truck hit the van?

by multiplying the van's speed by the truck's speed
by multiplying the van's mass by the truck's mass
by multiplying the van's mass by its acceleration
by multiplying the truck's mass by its velocity