Question

250 N force is required to raise 75 kg mass from a pulley. If rope is pulled 12 m then the load is lifted to 3m, the efficiency of pulley system will be : -

Answer 1

Load W= Mg=75×10=750N

Effort(P)= 250N

Mechanical advantage= Load÷effort= W/P =750/250=3.

Velocity ratio = distance travelled by effoet÷distance travelled by load = 12/3= 4

Efficiency n=Mechanical advantage÷Velocity ratio

                  =(3/4)×100= 75%

Answer 2

Efficiency of the pulley system = 73.58%

Explanation:

Given that in a pulley system, mass m = 75 kg and effort P = 250 N.

g is constant of gravitation (9.81 m/s2)

Load W = mass * gravity = 75 * 9.81 = 735.75

Mechanical advantage = Load / effort = W / P = 735.75 / 250 = 2.943

Velocity ratio = distance travelled by effort / distance travelled by load = 12 / 3 = 4

Efficiency of the pulley system = mechanical advantage / velocity ratio = 2.943 / 4 * 100 = 73.575%