Flywheels are large, massive wheels used to store energy. They can be spun up slowly, then the wheel's energy can be released quickly to accomplish a task that demands high power. An industrial flywheel has a 2.0 m diameter and a mass of 260 kg . Its maximum angular velocity is 1400 rpm .
- The flywheel is disconnected from the motor and connected to a machine to which it will deliver energy. Half the energy stored in the flywheel is delivered in 2.5 s . What is the average power delivered to the machine?
- How much torque does the flywheel exert on the machine?
The Attempt at a Solution
From working out earlier parts of the problem, I already have:
ω=1400rpm*(min/60s)*(2π rad/rev) = 146.61 rad/s
P = ΔE/Δt = ½Kmax/Δt = 1/8*m(ωr)2/Δt = 1/8*(260kg)*(146.61rad/s*1.0m)2 = 2.794*105 W
Mastering Physics marks this as correct. However, when I solve for torque in terms of power and angular velocity
τ = P/ω = 2.794*105 W / 146.61 rad/s = 1905.9 N*m
Master Physics marks 1900 N*m (it requires 2 significant figures), as incorrect. Any suggestions?