10. A skateboarder with a mass of 30 kg ends up with a final velocity of 7 m/s after a
push of 360 joules of work. What was the skateboarders initial velocity?

5 m/s

Explanation:

The net work is equal to change in kinetic energy hence

where m is the mass of the skateboarder, v is the speed and the subscripts i and v represent initial and final respectively. Substituting 7 m/s for final velocity and 30 for mass m then

b. lifting dumbbell weight at 20-degree angle from the body after a 45-degree angle