A300.0-kg speedboat is moving across a lake at 35.0 m/s. what is the momentum of the speedboat?

The momentum (n) of object is the product its mass (m) and velocity (v).
                                      n = m x v
Substituting the known values, 
                                      n = (300 kg) x (35 m/s) 
Thus, the value of the momentum is 10,500 kg m/s.