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CIE M1 MECHANICS Questions

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astarmathsandphysics:
A ball is thrown upwards with and initial velocity of 15.5. for how long is the ball higher than 10.5 metres?

Q2 ) A ball is thrown upwards with an initial velocity of 12 from a point 2.5 metres above the ground. find the time when the ball reaches the ground and the velocity of the ball at this instant.

Q1)s=ut+1/2at^2>10.5
15.5t-4.9t^2>10.5
0>4.9t^2-15.5t+10.5
t=0.98 or 2.18 so the ball is 105m above the ground at these times
ANS=2.18-0.98=1.2s

Q2)v^2=u^2+2as
v^2=12^2+2*-9.8*-2.5=193
v=-sqrt(193)=-13.9
t=(v-u)/a=(-13.9-13.9)/(-9.8)2.6 secs

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