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A particle is projected vertically upwards with a speed of 4...

A particle is projected vertically upwards with a speed of 40 m/s. At what times will it be 35m above its point of projection? Take g=10ms2

A.

1 sec and 7 sec

B.

1 sec and 8 sec

C.

2 sec and 5 sec

D.

2 sec and 7 sec

Correct answer is A

s=ut+12at2

s=ut12gt2 (Upward movement against gravity)

35=40t1210t2

35=40t5t2

5t240t+35=0

t28t+7=0

(t1)(t7)=0t=1 sec and 7 sec