Maths question help?!?

A gun is fired vertically with the end of the barrel 2m above the ground. The bullet leaves the barrel at 100m/s.



a) What is the maximum height above the ground the bullet reaches?



b)How long does the bullet remain 5m from the ground?



Help guys i have an exam to revise for and need to revise and learn the problems.



ThanksMaths question help?!?
qa

use the equation

Vf^2 = Vi^2 - 2gh

where h is the height from point of launch



since at max ht. velocity is zero,

0 = 100^2 - 2*9.8h

h = 510.2 m

and max height above the ground = 510.2 + 2

= 512.2 m

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qb

i presume ';5m from the ground';

means 5m or more from the ground

else the q has little meaning



consider the bullet falling from a height of 512.2 m, starting from rest

it falls a distance of (512.2 - 5)m = 507.2 m



use the equation

h = 0.5gt^2

507.2 = 0.5*9.8t^2

t = 10.174 s



now by symmetry, it would have taken the same time rising from 5 m to 512.2 m,

so time the bullet is 5 m (or more) above the ground

= 2*10.174

= 20.35 s

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