Help Solve Physics Problem Now: String Unwound from Wheel

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A string wound on a wheel with a 20 cm diameter is unwound at 75 cm/s, and the problem requires calculating the number of revolutions made when 9.0 m of string is unwound and the time taken for this process. To solve this, one must first determine the wheel's circumference, which is essential for calculating the number of revolutions. The second part involves using the formula for time, which relates distance and velocity. Participants are encouraged to show their work for better understanding and learning. This approach ensures clarity in solving similar physics problems in the future.
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A string wound on the rim of a wheel 20 cm in diameter is pulled out at a rate of 75 cm/s. Through how many revolutions will the wheel have turned by the time that 9.0m of string has been unwound? Also how long did it take?

I really need help with this. If you post, please show all work so I can learn how to do this type of problem.
 
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joecocobo, welcome to PF.

You'll have to follow the posting template and show your attempt at working on the problem before help/hints/guidance can be offered.
 

Homework Statement


A string wound on the rim of a wheel 20 cm in diameter is pulled out at a rate of 75 cm/s. Through how many revolutions will the wheel have turned by the time that 9.0m of string has been unwound? Also how long did it take?


Homework Equations


I don't know any equations to use


The Attempt at a Solution


I honestly don't know where to start, to even make an attempt
 
Last edited by a moderator:
You may be overthinking it. For starters, separate the question into its two components. They are not related.1] A 9.0m string is wound on the rim of a wheel 20 cm in diameter. How many times is the string wrapped around the wheel?
Do you know the relationship between the diameter of a circle and its circumference?

2] How long will a point on the string take, moving at 75cm/s, to travel 9.0m?
Do you know how to calculate time, given a distance and a velocity?
 
Last edited:
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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