88. A child pulls a cart to the left along a rough surface. Which one of the free body diagrams correctly depicts all the forces acting on the carrito?

Eje x

           fr- F = m a

eje y    

           N-W =0

Explanation:

Para este ejercicio, debemos usar la segunda ley de Newton, donde se necesita fija un sistema de referencia el mas usado es un sistema horizontal y vertical para los ejes x e y  

en el adjunto puede ver el diagrama de cuerpo libre correcto,  

las fuerza son

Eje x

           fr- F = m a

eje y    

           N-W =0

la ecuacion para la fuerza de roce es

          fr = my N

the independent variable, or the one that is intentionally manipulated is the speed.

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.