How far from a lens of focal length 50.0 mm must the object be ...

[jrubin]

How far from a lens of focal length 50.0 mm must the object be placed if it is to form a virtual image magnified in size by a factor of three?
 
  A) 33.3 mm
  B) 48.0 mm
  C) 38.3 mm
  D) 42.2 mm
  E) 54.4 mm

Question 2

A ballerina spins initially at 1.5 revolutions/second when her arms are extended. She then draws in her arms to her body and her moment of inertia becomes 0.88 kg-m2 and her angular speed increases to 4.0 rev/s.
 
  Determine her initial moment of inertia.

[juliaf]

Answer to Question 1

A

Answer to Question 2

2.3 kg  m2

[jrubin]

Thanks for the timely response, appreciate it

[yeungji]

Excellent