Hi everyone….well I have just started to learn about rotational motion, therefore, I am really confused so I have two different problems that I need help on.(adsbygoogle = window.adsbygoogle || []).push({});

1.) Q: A washing machine goes into the “spin cycle”. From rest the washer starts rotating, gaining 1 rev/sec of rotational velocity each second. How long before it is spinning at 300 RPM? What it its angular acceleration? How many revolutions does it go through in getting up to 300 RPM?

When the spin cycle ends the washer comes to rest from 300 RPM in 4 seconds. What it its angular acceleration? How many revolutions does it go through?

A: I think this is totally wrong but here it is:

300rev/1min * 1min/60sec = 5 rev/sec, so would that be 5 sec?

alpha = change omega/ time

omega = 5 rev/ 1sec * 2pi = 31.4rad/sec

(31.4-0)/5 = 6.26rads, which is not even in the right units, so I know it is wrong. I don’t even know how to broach this problem?

2.) Q:Two 5 kg masses are connected by an arm that measures 5 ft from end to end. In the middle of the arm is a low-friction pivot point. A lightweight pulley 2 ft in diameter is mounted at the pivot point, with a cord wrapped around the pulley. The cord is pulled with a steady 20 N tension.

How long before the masses achieve a tangential speed of 40 mph?

A: torque = m * r^2 * alpha

20kgm/s^2 = 10kg * 1.83^2 * alpha

alpha = .597m/s^2

40mph = 17.88m/s

acceleration = change speed/ time

.597m/s^2=(17.88m/s-0m/s)/t = 30.8s

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# Rotational motion of a washing machine

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