Question

Juan draws a free-body diagram of an object that is in dynamic equilibrium moving to the left.

A free body diagram with 4 force vectors. The first vector is pointing downward, labeled F Subscript g Baseline = Y. The second vector is pointing right, labeled F Subscript t Baseline = X. The third vector is pointing upward, labeled F Subscript N Baseline = 45 N. The fourth vector is pointing left, labeled F Subscript f Baseline = negative 30 N. The up and down vectors are the same length. The right and left vectors are the same length.

Which labels correctly complete the diagram?

X: 45 N
Y: –45 N
X: –45 N
Y: 30 N
X: 30 N
Y: –45 N
X: 30 N
Y: –30 N

Answer 1

X = 30 N and Y = −45 N.

Reason: dynamic equilibrium ⇒ net force = 0. Horizontally, the leftward force is −30 N so the rightward force must be +30 N. Vertically, the upward normal is +45 N so gravity must be −45 N to balance it.