Question

A rock weighing 20N falls from a height of 16m and sinks 0.6m into the ground.From energy considerations,find the average force f between the rock and the ground as the rock sinks.

Answer 1

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➧ sᴜᴘᴘᴏsᴇ ᴛʜᴇ ʜɪɢʜᴇsᴛ ᴘᴏɪɴᴛ ғʀᴏᴍ ᴡʜɪᴄʜ ᴛʜᴇ ʀᴏᴄᴋ ғᴀʟʟs ɪs ᴀ ᴀɴᴅ ʙ ɪs ᴛʜᴇ ᴘᴏɪɴᴛ ɪɴᴛᴏ ᴛʜᴇ ɢʀᴏᴜɴᴅ ᴡʜᴇʀᴇ ɪᴛ sɪɴᴋs.

➧ ɴᴏᴡ,

h = 16 m & h' = 0.6 m

➧ (ᴀ ɴᴏɴ ᴄᴏɴsᴇʀᴠᴀᴛɪᴠᴇ ᴡᴏʀᴋ ɪs ᴅᴏɴᴇ ᴏɴ ᴛʜᴇ ʀᴏᴄᴋ ʙᴇᴛᴡᴇᴇɴ ᴀ ᴀɴᴅ ʙ).

➧ ᴛʜɪs ᴡᴏʀᴋ ɪs ɢɪᴠᴇɴ ʙʏ,

W' ➾ -f h' & dK + dU = W'

0 + [mg (-h') -mgh] = -fh'

or, f ➾ mg (h + h') / h'

➾ 20 x (16 + 0.6) / 0.6

➾ 553 N...✔

Answer 2

heya..

here is you answer..

Suppose the highest point from which the rock falls is A and B is the point into the ground where it sinks.

Now, h=16 m and h'=0.6 m

A non conservative work is done on the rock between A and B.

This work is given by,

W'=-f h'

and dK+dU=W'

0+ [mg (-h') -mgh]=-fh'

or f=mg (h+h') / h'

=20 x (16+0.6) /0.6

=553 N

It may help you...☺☺