Answer:
i) 21 cm
ii) At infinity behind the lens.
iii) A virtual, upright, enlarged image behind the object
Explanation:
First identify,
object distance (u) = 42 cm (distance between object and lens, 50 cm - 8 cm)
image distance (v) = 42 cm (distance between image and lens, 92 cm - 50 cm)
The lens formula,

Then applying the new Cartesian sign convention to it,

Where f is (-), u is (+) and v is (-) in all 3 cases. (If not values with signs have to considered, this method that need will not arise)
Substituting values you get,
i) 
f = 21 cm
ii) u =21 cm, f = 21 cm v = ?
Substituting in same equation
v ⇒ ∞ and image will form behind the lens
iii) Now the object will be within the focal length of the lens. So like in the attachment, a virtual, upright, enlarged image behind the object.
The answer is a. over use of petroleum
Answer:
b mixtures or substances
Explanation:
i seasrced
the web that is the anwer i got
Answer:
B
Explanation:
a force acting upon an object increases that objects acceleration
Answer:Kinetic energy is the energy of motion. All moving objects have kinetic energy. When an object is in motion, it changes its position by moving in a direction: up, down, forward, or backward. 3. A force is a push or pull that causes an object to move, change direction, change speed, or stop.
Explanation: Not sure if that's what you meant but that's the answer I can give you.