- #1
MusePhysick
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Homework Statement
An object fired with a velocity of Vo covers a verticle distance of 20.0m and a horizontal distance of 25.0m in the 4th second of its motion. Determine the following:
a) Its velocity of projection, Vo
(the rest I am not going to worry about cos if i get part a) started then i should be fine i just don't know what I am doing wrong)
Homework Equations
ucosθ = x
usinθ = y
v = u + at2
s = ut + 1/2at2
v2 = u2 + 2as
v = s/t
The Attempt at a Solution
ok so I've tried many a times but i think i have a misconception or not seeing what is happening etc.
i know the answer as it is given which is Vo = 59.8 m/s 65.3o (angle between ground and vector)
so it takes 4 seconds for the projectile to be displaced horizontally by 25 m
so by v=s/t
v=25/4
v=6.25
which v is also known as x
so i have x=6.25 m/s
the verticle velocity i found by many ways or tried to but here's one way
s=ut + 1/2at2
s = 20
a = -9.8
t = 4
20 = 4u + 1/2.(9.8).42
98.4 = 4u
u = 24.6 m/s
and in this case u = y
so y=24.6
by pythagoras
Vo2 = y2 + x2
Vo2 = 24.62 + 6.252
Vo = 25.2815
clearly not the answer but i proceeded to find the angle
y = usinθ
θ = 14.255
angle between ground and vector = 90 - 14.255
angle = 75.745 degrees
which is clearly not the case
if you see where I've gone wrong please do tell :)
ive tried many many wasy of getting the projected velocity and nothing seemed to work, I've tried 4 times and that takes a long time