John's face is 20 cm in front of a concave shaving mirror. If he observes his image to be twice as big and erect, what is the focal length of the mirror?

A)

10 cm
B)

20 cm
C)

30 cm
D)

40 cm
E)

50 cm


D

Physics & Space Science

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A hydraulic press multiplies a force by 100, which is compensated by

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