physics qtn
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an object is accelerated uniformly from rest and travel 20m in 8.0s
calculate
i)average speed of the body in this 8.0s
ii)the speed after 8s
iii)acceleration
need help with the one in bold.
a man psuhes a box of mass 20kg across a horizontal surface at a constant speed by applying a force of 40N
i)what is the weight of the box?
ii)what is the fictional force acting on the box? -
Originally posted by Y_Shun:
hmmm i duno but i can find acceleration first
an object is accelerated uniformly from rest and travel 20m in 8.0s
calculate
i)average speed of the body in this 8.0s
[b]ii)the speed after 8s
iii)acceleration
need help with the one in bold.
a man psuhes a box of mass 20kg across a horizontal surface at a constant speed by applying a force of 40N
i)what is the weight of the box?
ii)what is the fictional force acting on the box?[/b]
2nd one: 40N loh....since is constant speed means no resultant force
then the man is the onli horizontal force besides friction so force applied muz b equal to friction -
if i am not wrong, if you cant understand anything, apply the formula...at least that's what some pple did in O levels.
v=u+at
v^2=u^2+2as
s=ut+0.5at^2
these formulas can be applied when the acceleration is constant.
(a) is easy.
next you calculate (c) first.
s=ut+0.5at^2
20=0.5a8^2
a=0.625m/s^2
then (b) v^2=u^2 + 2as
v^2=0+2(0.625)(20)
v^2=25
v=5m/s -
neber learn those formulas before leh...did so in AMATHS, but in the end heard not in syllabus liao. then physics never teach.
btw it shld be combined physics -
btw do we need to know what violet light, blue light, red light????
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Originally posted by Y_Shun:
speed is distance over time
an object is accelerated uniformly from rest and travel 20m in 8.0s
calculate
i)average speed of the body in this 8.0s
[b]ii)the speed after 8s
iii)acceleration
need help with the one in bold.
a man psuhes a box of mass 20kg across a horizontal surface at a constant speed by applying a force of 40N
i)what is the weight of the box?
ii)what is the fictional force acting on the box?[/b] -
U can try drawing a velocity vs time graph to solve this problem.Originally posted by Y_Shun:neber learn those formulas before leh...did so in AMATHS, but in the end heard not in syllabus liao. then physics never teach.
btw it shld be combined physics
Since acceleration is constant, gradient of the graph is constant.
It will be a diagonal line going upwards as speed increases uniformly when time increases.
Displacement travelled by the object is equivalent to the area under the graph. So basically, it is just an application of your knowledge of finding area of triangles. -
Their similarity and differences?Originally posted by Y_Shun:btw do we need to know what violet light, blue light, red light????
Similarity: Speed
Differences: Wavelength, Frequency -
didnt he say "accelerated uniformly"? if thats so wouldnt the accel be a diagonal line? im nt very sure abt this too, but i think constant accel is not equal to uniform accel?
oh and for the light rays...my teacher said...if u shine different coloured waves into a prism, u'll get different refractive indexes for the prism for each different coloured light eh(proven in the scattering of light i think). so by the formula n= speed of light in vacuo/ speed of light in medium, shouldnt their speeds be different? thats what i think, need clarification... -
Originally posted by Y_Shun:
1st question: use the kinematics equation then can find lor.
an object is accelerated uniformly from rest and travel 20m in 8.0s
calculate
i)average speed of the body in this 8.0s
[b]ii)the speed after 8s
iii)acceleration
need help with the one in bold.
a man psuhes a box of mass 20kg across a horizontal surface at a constant speed by applying a force of 40N
i)what is the weight of the box?
ii)what is the fictional force acting on the box?[/b]
2nd question: weight of box = normal force, normal force x coefficient of friction, wait is that right, cant remember. wait nvm, since constant speed, means force of friction is 40N.