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traviata

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## Homework Statement

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?

## Homework Equations

P=τ⋅ω

## 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 = ½K

_{max}/Δt = 1/8*m(ωr)

^{2}/Δt = 1/8*(260kg)*(146.61rad/s*1.0m)

^{2}= 2.794*10

^{5}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*10

^{5}W / 146.61 rad/s = 1905.9 N*m

Master Physics marks 1900 N*m (it requires 2 significant figures), as incorrect. Any suggestions?