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.
If something is going down a hill it can help slow it down
it can stop you from flying off a rollercoaster
If I can't open the lid of a jelly jar, I'd keep trying and if I can't open the lid of a jelly jar after the MANY tries I took, I'd ask for help.
The equation to work out the speed is distance/time.
If we apply this equation to your numbers we will first need to find the total distance travelled.
80km/h for an hour means you travel 80km
40km/h for 2 hours means you will travel 80km
80+80 is 160km in total.
The time taken to complete this distance is 3 hours so, applying the equation we get
speed = 160/3 = 52.33km/h