Lee majors, a professional stuntman, is preparing to run off a dock and dive into a large kayak. the stuntman has a mass of 80.8kg and the kayak has a mass of 29.9kg. if lee dives horizontally with a velocity of 5. what is his velocity in ms immediately after he jumps into the kayak? to simplify things, ignore any velocities in the y-direction.

4.01 m/s  
The is a conservation of momentum problem. The stuntman's momentum plus that of the kayak will remain constant. Since the momentum of the kayak is 0 at the beginning, we need to calculate what the momentum will be the moment after the stuntman lands in the kayak. We will consider the landing to be a non-elastic collision. 
Initial momentum 
80.8 kg * 5.50 m/s = 444.4 kg*m/s
 Total mass of stuntman and kayak
 80.8 kg + 29.9 kg = 110.7 kg
 Speed of kayak and stuntman
 444.4 kg*m/s / 110.7 kg = 4.014453478 m/s

  Rounding to 3 significant figures gives 4.01 m/s

I think it is D. I'm not sure though.