34.  “Rocket Man” has a propulsion unit strapped to his back. He starts from rest on the ground, fires the unit, and accelerates straight upward. At a height of 16 m, his speed is

5.0 m/s. His mass, including the propulsion unit, has the approximately constant value of

136 kg. Find the work done by the force generated by the propulsion unit.

The force generated by the propulsion unit is a non-conservative force.  Therefore the modified work-energy theorem is appropriate here.

 

Assuming the ground is height = 0, the initial potential energy is zero. Since he is starting form rest, his initial kinetic energy is also zero.  So the work done is

 

 

 

 

Alternatively we could

 

Solving for the thrust force

Finding the work done by the thrust

Now we need to determine ay

 

Since he started from rest.  Solve for ay

 

 

 

 

 

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This page last updated on January 11, 2020