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Atoms And Molecules

Question
CBSEENSC9006111

A car falls off a ledge and drops to the ground in 0.5 second. Let g = 10 ms–2.
(i) What is its speed on striking the ground?
(ii) What is its average speed during the 0.5 second?
(iii) How high is the ledge from the ground?

Solution

Given comma space

Time space taken space by space the space car space to space fall space on space ground comma space straight t space equals space 0.5 space straight s

Initial space velocity comma space straight u space equals space 0 space straight m divided by straight s

Acceleration space due space to space gravity comma space straight g space equals space minus space 10 space straight m divided by straight s squared

straight i right parenthesis thin space Speed space on space striking space the space groun d space is comma space
      straight v space equals space straight u space plus space g t space space left square bracket Using space 1 st space equation space of space motion right square bracket
space space space equals space 0 space minus space 10 space cross times 1 half space
space space space equals negative 5 space m s to the power of negative 2 end exponent         
The space negative space sign space shows space that space the space car space is space moving space downwards. space

ii right parenthesis thin space Average space speed comma space straight v space equals space fraction numerator straight u space plus space straight v over denominator 2 end fraction
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator 0 plus 5 over denominator 2 end fraction
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals 2.5 space straight m divided by straight s

iii right parenthesis thin space Height space of space the space ledge space from space the space ground space equals space distance
travelled space by space the space car. space
straight h space equals space straight s space equals space u t plus 1 half g t squared
space space space space space space space space space space space equals 0 space cross times 1 half plus 1 half cross times left parenthesis 10 right parenthesis cross times open parentheses 1 half close parentheses squared
space space space space space space space space space space space equals negative 1.25 space straight m 

The negative sign in the distance implies that the car is moving downwards.