6. Intro to Forces (Dynamics)

Which of the options is NOT an action-reaction pair in the following situation? A book slides across the floor, slowing down due to friction.

Boxes $A$ and $B$ are in contact on a horizontal, frictionless surface (Fig. E$4.23$). Box $A$ has mass $20.0$ kg and box $B$ has mass $5.0$ kg. A horizontal force of $250$ N is exerted on box $A$. What is the magnitude of the force that box $A$ exerts on box $B$?

World-class sprinters can accelerate out of the starting blocks with an acceleration that is nearly horizontal and has magnitude $15$ m/s². How much horizontal force must a $55$-kg sprinter exert on the starting blocks to produce this acceleration? Which body exerts the force that propels the sprinter: the blocks or the sprinter herself?

A small car of mass $380$ kg is pushing a large truck of mass $900$ kg due east on a level road. The car exerts a horizontal force of $1600$ N on the truck. What is the magnitude of the force that the truck exerts on the car?

An 85 kg cheerleader stands on a scale that reads in kg. What does the scale read if the 85 kg cheerleader lifts the 50 kg cheerleader upward with an acceleration of 2.0 m/s²?