A woman pulls her daughter on a sled by a rope on level, packed snow. The woman is 70 kg with red hair, earnest looking. The daughter is 20 kg with brown hair and wild curls. The sled is a Firestone-200 of mass 10 kg which slides along the snow with a coefficient of friction 0.09. The tension in the rope is 30 N, making an angle of 30˚ with the ground. They are going a constant 2.5 m/s for 4 s. (Use g = 10 m/s2.)
What is the work done by the normal force on the sled?