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? asked in Science & MathematicsPhysics · 1 decade ago

Angular speed question...? <repeat?

A car is moving at a rate of 65 miles per hour, and the diameter of its wheels is 2.5 feet.

(a) Find the number of revolutions per minute the wheels are rotating.

(b) Find the angular speed of the wheels in radians per minute

so..

Speed=65mph

D=2.5ft, r=1.25ft

Then for the formulas..

Linear speed=(arclength)/(time)

Angular speed=(theta)/(time)

Arclength=r(theta), theta=(Arclength)/r

The answers for

(a) 728.3 revolutions per minute

(b) 4576 radians per minute

I want to know how they got those because my answers come up very low compared to these.. and i'm using all of the formulas above, am i missing something?

This is a repeated question because the answers i got, didn't even answer the question correctly, just implied the answer approached the answer's quantity, if so explain this, because i'm pretty stumped.

1 Answer

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  • ?
    Lv 7
    1 decade ago
    Favorite Answer

    65 (mi/hr) *5280 (ft/mi)*(1hr/60min) = 5720 ft/min

    Rev/min = (ft/min)*(rev / ft) = 5720*(1rev / 2.5π) = 728.3 rev/min

    Rad/min = (rev/min)*(2π rad/rev) = 728.3*(2π) = 4576 rad/min

    Your problem is likely with the English system of weights & measures; nothing works without some weird conversion factor.

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