Two mating spur gears have 40 and 120 teeth respectively.

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

1. 6.6 Nm
2. 20 Nm
3. 40 Nm
4. 60 Nm

Correct Option: D

We know

		N_p	=	T_G
		N_G		T_p

where,
N_p = speed of pinion,
N_G = speed of gear wheel
T_G = number of teeth of gear,
T_p = number of teeth of pinion

∴		1200	=	120
		N_G		40

or N_G =400 r.p.m.
Since power transmitted by both gear will be equal
i.e. T_pω_p = T_Gω_G
where,
T_p = torque transmited by pinion
T_G = torque transmitted by gear wheel

∴		20 × 2π × 1200	=	T_G × 2π × 400
		60		60

∴ Torque transmitted by gear, T_G = 60 N-m.