Dan is gliding on his skateboard at 4.00 m/s . He suddenly jumps backward off the skateboard, kicking the skateboard forward at 6.00 m/s (as measured by an observer on the ground). Dan's mass is 60.0 kg and the skateboard's mass is 5.00 kg . How fast is Dan going as his feet hit the ground?
m/s.

The speed of the Dan is 38.33 m/s.                        

Explanation:

Given that,

Mass of Dan, m = 60 kg

Mass of skateboard, m' = 5 kg

Initial speed of Dan and skateboard is, u = 4 m/s

He suddenly jumps backward off the skateboard. The skateboard kicks forward at a speed of 6 m/s, v' = 6 m/s

We need to find the speed of Dan as his feet hit the ground. In the whole process, the momentum remains conserved. Let v is the speed of Dan. Using conservation of linear momentum as :

So, the speed of the Dan is 38.33 m/s.