Problem: Large brushes are desired for a larger brush contact area to maximize motor output, but small brushes are desired for low mass to maximize the speed at which the motor can run without the brushes excessively bouncing and sparking. (Small brushes are also desirable for lower cost.) Stiffer brush springs can also be used to make brushes of a given mass work at a higher speed, but at the cost of greater friction losses (lower efficiency) and accelerated brush and commutator wear. Therefore, DC motor brush design entails a trade-off between output power, speed, and efficiency/wear.
 What type of brushes are not the cheapest?
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Answer: unanswerable


Problem: At the start of her reign Victoria was popular, but her reputation suffered in an 1839 court intrigue when one of her mother's ladies-in-waiting, Lady Flora Hastings, developed an abdominal growth that was widely rumoured to be an out-of-wedlock pregnancy by Sir John Conroy. Victoria believed the rumours. She hated Conroy, and despised "that odious Lady Flora", because she had conspired with Conroy and the Duchess of Kent in the Kensington System. At first, Lady Flora refused to submit to a naked medical examination, until in mid-February she eventually agreed, and was found to be a virgin. Conroy, the Hastings family and the opposition Tories organised a press campaign implicating the Queen in the spreading of false rumours about Lady Flora. When Lady Flora died in July, the post-mortem revealed a large tumour on her liver that had distended her abdomen. At public appearances, Victoria was hissed and jeered as "Mrs. Melbourne".
With whom did Lady Flora consipire against Queen Victoria? 
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Answer: Conroy and the Duchess of Kent


Problem: In response to the early-to-mid-17th century "continental rationalism" John Locke (1632–1704) proposed in An Essay Concerning Human Understanding (1689) a very influential view wherein the only knowledge humans can have is a posteriori, i.e., based upon experience. Locke is famously attributed with holding the proposition that the human mind is a tabula rasa, a "blank tablet", in Locke's words "white paper", on which the experiences derived from sense impressions as a person's life proceeds are written. There are two sources of our ideas: sensation and reflection. In both cases, a distinction is made between simple and complex ideas. The former are unanalysable, and are broken down into primary and secondary qualities. Primary qualities are essential for the object in question to be what it is. Without specific primary qualities, an object would not be what it is. For example, an apple is an apple because of the arrangement of its atomic structure. If an apple was structured differently, it would cease to be an apple. Secondary qualities are the sensory information we can perceive from its primary qualities. For example, an apple can be perceived in various colours, sizes, and textures but it is still identified as an apple. Therefore, its primary qualities dictate what the object essentially is, while its secondary qualities define its attributes. Complex ideas combine simple ones, and divide into substances, modes, and relations. According to Locke, our knowledge of things is a perception of ideas that are in accordance or discordance with each other, which is very different from the quest for certainty of Descartes.
What did Descarte call our knowledge of things?
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Answer:
unanswerable