Which of the following is a closed system or very close to a closed system? a. a block of iron sealed in a vacuum chamber b. a dish of ice cream sitting in the sunlight c. a stick of dynamite during an explosion d. a stalled car in a snowstorm

12. ritu obtained a distinct image of a distant tree on the screen with the of a concave mirror.to find the focal length of the mirror she has to measure the distance between: (a) mirror and the tree. (b) screen and the tree.(c) mirror and the screen. (d) mirror and tree as well as between screen and the tree.