# Solve these numericals:- (PLEASE HELP, URGENTLY NEEDED!) 1) A certain force exerted for 1.2 seconds raises the speed of an object from 1.8 metres per second to 4.2 metres per second. Later the same force is applied for 2 seconds. How much does the speed change in two seconds? 2) A body is released from a height of 20 metres. Calculate the final velocity of the body (take g = 10 metres per second square).

1
by reishumwi

2015-04-30T18:07:01+05:30

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1)  Force = F        so acceleration a = F/m
a = (v - u) / t  = (4.2 - 1.8) / 1.2 = 2 m/sec²

since same force is applied again, the same acceleration happens.
v = u + a t    =>    v - u = a t = 2 m/sec² * 2sec =  4 m/sec

change in speed = 4 m/s

2)    s = 20 meters. = displacement
v² = u² + 2 a s            -- equation of motion under gravity,  a = + g
v² = 0 + 2 g s    =  2 * 10 * 20

v = 20 m/sec  = final velocity