Question

Two mating spur gears have 40 and 120 teeth respectively. The pinion rotates at 1200 rpm and transmits a torque of 20 Nm. The torque transmitted by the gear is

(a) 6.6 Nm

(b) 20 Nm

(c) 40 Nm

(d) 60Nm

The question was posed to me by my school teacher while I was bunking the class.

The question is from Standard Spur Gears in portion Toothed Gearing & Gear Trains of Machine Kinematics

Answer 1

The correct option is (d) 60Nm

To elaborate: We know, N1/N2 = T1/T2

N1 = speed of pinion

N2 = speed of gear wheel

T1 = number of teeth of gear

T2 = number of teeth of pinion

1200/N2 = 120/40

N2 = 400 r.p.m.

Since power transmitted by both gear will be equal

T1ω12 x ω2

torque transmitted by gear, = 60 N-m.