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# A particle is projected vertically upwards from a roof of a tower 60 m high with velocity 20 m/s. Find the average speed upto an instant when it strikes the ground. g = 10 m/s(sq)

11 years ago

let T1 be the time taken by the particle to reach at the highest point

applying v=u-gT1  , v=0at the highest point ,u=20m/sec

T1=2sec

let S1 be the distance covered during this period

then S1 = uT1-(gT1^2)/2

S1=20m

same time is taken by particle to come at the point of projection

now the velocity of particle becomes 20m/sec in downward dyrection

let time taken by particle to raech the ground is T2,again applying eq of motion

-60=-20T2-(gT2^2)/2

T2=2sec

total time =2T1+T2=6sec

total distance=60+2.20=100

average speed =100/6=16.67m/s

2 years ago
A block moves ina straight line with velocity v for time t°.then it's velocity becomes 2vfor next t° of ime finally it's velocity becomes 3v for timeT.if average velocity during the complete journey was2.5v then find T in terms of t°