A stone is dropped from the peak of a hill. It covers a distance of 30 m in last second of its motion. What is height of peak?

1 Answer
P dilip_k
May 13, 2017

Let the height of the peak be #h# m and the stone dropped from the peak takes #t# sec to reach the ground. It also covers #30#m in the last sec i.e. t th sec.
Taking acceleration due to gravity #g =9.8m"/"s^2#and initial velocity #u=0# we can write applying equation of motion under gravity. In

#h=0xxt+1/2xxgxxt^2.......[1]#

#30=0+1/2xxg(2t-1).....[2]#

From equation [2] we have

#30=1/2xx9.8(2t-1)#

#=>2t-1=30/4.9#

#=>2t=30/4.9+1#

#=>t~~3.56 s#

Inserting the value of #t=3.56 s# in [1]

we get

#h=1/2xxgxxt^2=1/2xx9.8xx3.56^2~~62.1m#

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