From the top of a cliff 50m above sea level, a stone is thrown vertically upwards with a velocity of 15m/s. After how many seconds and with what velocity will it hit the sea?

S=ut - 1/2gt"2..{against gravity}.

15t =5t"2..t=0 or 3..t=3s. or 2u/g=3s.

V=0 + gt=10 x 3=30m/s

or

Given,

Initial velocity in upwards direction (u) = -15m/s

Acceleration (a) = 10 m/s2

Distance (s) = 50 m

Final velocity (v) =?

Time taken (t) =?

………..

Final velocity,

2as = v2-u2

2 (10) (50) = (v) 2 – (-15)2

1000 = v2 – 225

1000+225 = v2

1225 = v2

35 = v

Therefore final velocity = 35 m/s

………………..

Time taken,

V=u+at

35=-15+10.t

35+15=10t

50=10t

50/10=t

5=t

Therefore time taken = 5 sec.

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