Question

A particle passes a given point moving downward with a velocity of 50 m/s. How long before this was it moving upward at the same rate?
(1) 12 s
(2) 18.2 s
(3) 10.2 s
(4) 15.4 s​

Answer 1

Answer:

The velocity at the start of the journey is 50m/s so we can find the maximum height at which the particle has traveled.

According to newton laws of motion.

u^2=2gh.

50*50 = 2*10*h.

h= 125m.

So, the maximum height traveled by the particle is 125m.

Thus time taken to reach at 125m will be.

As, h = ut + 1/2gt^2.

125 = 50t - 5t^2.  

t^2 - 10t + 25 =0.

(t-5)^2 = 0.

So, t=5 sec

Thus, now the particle after the maximum height has traveled upto reaching the speed of 50m/s.

v=u + at.

50=10*t.

t=5.

Thus, total time traveled will be 5*2 = 10sec.

Answer 2

Answer:

hey see the attached solution