Forces: Newton's Laws

Question

An elevator of mass 800 kg accelerates at 3.0m/s^2[down]. What force does the cable exert on the elevator?

Answer 1

F = upward tension in the cable

 

Assuming up is positive and down is negative,

 

a = -3.0 m/s²

 

F - mg = ma ⇒

 

F = m(a + g) = (800 kg)[(-3.0 + 9.8) m/s²] = 5440 N (up)