Question

8)How much joules of energy is needed to change the speed of a 2,000 kg sport utility vehicle from 20.0 m/s to 30.0 m/s?

9) A rope exerts a force on a 20.0-kg crate. The crate starts from rest and accelerates upward at 2.10 m/s2 near the surface of the earth.

How much work was done by the force in raising the crate 3.30 m above the floor?

Answer 1

8) Minimum Energy needed = 0.5*m*(vf^2 - vi^2)

                                         = 0.5*2000*(30^2 - 20^2)

                                        = 500000 J = 5*10^5 J --> Answer

9) m*a = F - m*g

=> F = m*(a+g)

      = 20*(2.1+9.8)

      = 238 N

W = F*d

   = 238*3.3

= 785.4 J = 0.785 kJ --> Answer