The momentum of the car is equal to:
[tex]p=mv=(1800 kg)(5.6 m/s)=10080 kg m/s[/tex]
We need to find the new speed v at which the new system (bycicle+rider) have same momentum p of the car. The mass M of the new system is M=120 kg. Using the value of momentum we found previously and the same formula for the momentum, we find
[tex]v= \frac{p}{M}= \frac{10080 kgm/s}{120 kg}=84 m/s [/tex]
So, the speed of the bycicle must be 84 m/s.
