Dan is gliding on his skateboard at 4.00 m/s . he suddenly jumps backward off the skateboard, kicking the skateboard forward at 8.00 m/s . dan's mass is 50.0 kg and the skateboard's mass is 7.00 kg .

v₂ = 3.44 m/s

Explanation:

given,                                                

Dan is gliding on skateboard at = 4 m/s

speed of skateboard = 8 m/s              

mass of Dan = 50 Kg                                

mass of skateboard = 7 Kg                            

Speed of Dan when his feet hit the ground = ?

Using conservation of momentum            

       PE(initial) = PE(final)                              

       (M+m)V = m v₁ + M v₂                  

       (50+7)x 4 = 7 x 8 + 50 x v₂        

       50 x v₂ =172                              

            v₂ = 3.44 m/s                  

speed of Dan when his feet hit the ground = v₂ = 3.44 m/s