Question

An insect crawling up a wall crawls 6 cm up in first
second and then slides 4 cm down in next second. It
again crawls up 6 cm in third second and again
slides 4 cm downwards in 4th second. How long will
insect take to reach a hole in wall at a vertical height
of 24 cm from starting point?
20 s
0 27 s
25 s
0 19 s​

Answer 1

Answer:

19 s

Explanation:

as per the question, the insects crawls 1cm per sec

so till 17 sec it's will reach 18cm

in the 19th sec, it will crawl 6cm which is 18cm +6cm = 24cm

19th sec it will reach so it doesn't fall back

Answer 2

Given :  An insect crawling up a wall crawls 6 cm up in first second and then slides 4 cm down in next second.

It again crawls up 6 cm in third second and again slides 4 cm downwards in 4th second.

To Find :  How long will insect take to reach a hole in wall at a vertical height of 24 cm from starting point

20 s

27 s

25 s

19 s​

Solution:

crawls 6 cm up in first second and then slides 4 cm down in next second.

=> in 2 secs       ,  it goes up by   4 - 2  =  2 cm

Distance of 2 cm   in 2 secs

=> on average 1 cm every sec

at first it looks like it will take 24 sec to go 24 cm  

but once insect reach 24 cm ( in hole ) then it will not slide back

Hence 24 - 6 = 18 cm    , So time taken would be  

time taken to reach 18 cm  and then 1 more sec to reach 24 cm

it will take 18  sec to go 18 cm  

Hence Total time taken = 18  +  1     =  19 secs

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