Some physics qn
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1) I still dont understand the difference bewteen displacement and distance.
if the point of orgin is x.
y-----------------------------x-----------------------------z
car moves from x to z then to y. Which part of the displacement is negative?
Next, if you talk about car moving ard in circles. will the displacement be negative?
lol ..
how do you convert picogram^2 to kg^2
Do you need to care about the square(^2) or just simply convert picogram into kg.
next: a machine shoots a ball vertically upwards. If the ball takes 3s to reach the highest point, what is the distance travelled by the ball when t=1?
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Originally posted by davidche:
1) I still dont understand the difference bewteen displacement and distance.
if the point of orgin is x.
y-----------------------------x-----------------------------z
car moves from x to z then to y. Which part of the displacement is negative?
Next, if you talk about car moving ard in circles. will the displacement be negative?
hi sorry accidentally clicked edit instead of quote. could you retype q2
if you treat going from x to z as positive, then going from z to y would be negative. it's with respect to x as the starting point..
for circular motion, displacement is the change in angular velocity. it depends on how you define your angle - clockwise or anti-clockwise.
but for sec 4 lvl you can heck care
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hi da jie
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Originally posted by bryanw:
hi da jie
hi.. ugh.. the cons of being a moderator.. i keep clicking edit instead -
done. And i added another qn too. I think i kinda suck in kinematics. Pls tell me if the qn is not in syllabus.. Now i am doing all the 3 finger qns in the 1001 physics qn book btw.
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how do you convert picogram^2 to kg^2
Do you need to care about the square(^2) or just simply convert picogram into kg.
yes you need to care abt the square.
1 picogram = 10^-12 gram = 10^-15 kg
1 picogram^2 = (10^-15)^2 kg
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next: a machine shoots a ball vertically upwards. If the ball takes 3s to reach the highest point, what is the distance travelled by the ball when t=1?
V = Vo + at
X - Xo = Vot + .5at2
v2 = vo2 + 2a(X - Xo)
X - Xo = .5(Vo + V)t
a = 9.8, t = 3, V = 0
Find Vo then find X or whichever way you want to start with.
p.s. you learnt these equations right
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freak. firstly that formula shld not be tested since it isnt in syllabus.
I hate these stupid qns. They think they are pro by testing out of syllabus.
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oh oops.. u sec 4 ah? i go see what's the sec 4 method
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Originally posted by davidche:
1) I still dont understand the difference bewteen displacement and distance.
if the point of orgin is x.
y-----------------------------x-----------------------------z
car moves from x to z then to y. Which part of the displacement is negative?
Next, if you talk about car moving ard in circles. will the displacement be negative?
lol ..
how do you convert picogram^2 to kg^2
Do you need to care about the square(^2) or just simply convert picogram into kg.
next: a machine shoots a ball vertically upwards. If the ball takes 3s to reach the highest point, what is the distance travelled by the ball when t=1?
1) Displacement is a vector, means has magnitude and direction
Distance is a scalar, means only has magnitude.
Whether y or z is positive or negative displacement depends on where you are pointing as positive. You have to choose a direction.
if a car moves in circles, u hv both vertical and horizontal displacements. Again, it depends from which position you want to define as positive or negative
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next: a machine shoots a ball vertically upwards. If the ball takes 3s to reach the highest point, what is the distance travelled by the ball when t=1?
longer method:
draw the v-t graph
Starting vel = u,
and when vel = 0, t = 3
So you calculate gradient... (u-0)/3 = 10
u = 30 m/sso when t =1, use gradient again
(30 - v) /1 = 10
v = 20so area of trapezium under graph
= 0.5 * (30 + 20) * 1
= 25 m -
Originally posted by eagle:
1) Displacement is a vector, means has magnitude and direction
Distance is a scalar, means only has magnitude.
eagle kor kor pls answer for me.. i'm very noob -
Originally posted by eagle:
longer method:
draw the v-t graph
Starting vel = u,
and when vel = 0, t = 3
So you calculate gradient... (u-0)/3 = 10
u = 30 m/sso when t =1, use gradient again
(30 - v) /1 = 10
v = 20so area of trapezium under graph
= 0.5 * (30 + 20) * 1
= 25 m
omg!!! totally understood liao. Thanks -
The way i do:
6N(0.2m) + 10N(0.4m) = 5.2
which is wrong.
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where did your values come from?
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omg got it . Its 6 N. wonderful qn testing on concepts. haha. Work is done all the way so 10N(0.6m). Not just WD to overcome friction or WD to move.
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Which wave is useful for night vision gogglesChoose one answer.
a. visible light b. radio wave c. gamma radiation d. infra red 
why is this so argh?
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Originally posted by eagle:
where did your values come from?
from the picture
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as far as i know from army, night vision goggles work on 2 principles
1) Infra-red rays, to see heat emitting from pple, machines, buildings, tanks, etc
2) Some electrons bombarding some zinc dunno what thing... this one very cheem... I also dunno
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Originally posted by davidche:
from the picture
can't see any picture... but anyway... u solved it... so ok :D
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Want to ask. If the rheostat resistance is increased, more current flows through the bulb thus would the brightness of bulb increase?
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yo can see the pic?
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can u upload to photobucket or imageshack or xs.to instead?
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done. just look at the circuit can liao.
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can view the pic?