Answer:
d) Gravity, a normal force, and kinetic friction
Step-by-step explanation:
- When the bobsledder pushes her sled across horizontal snow to get it going, after she jumps into the sled there acts a force of gravity on the total mass of the sled including the bobsledder.
- The sled moves horizontally and not vertically this means that there is a normal force acting in the vertically upward direction opposite to the gravity.
- While the sled moves on the horizontal surface and comes to the rest there acts a kinetic frictional force on the body in the direction opposite to the direction of motion.