physics qtn

Y_Shun SG

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?

darkhour SG

Originally posted by Y_Shun:
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]

hmmm i duno but i can find acceleration first Laughing

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

HyuugaNeji SG

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

Y_Shun SG

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

Y_Shun SG

btw do we need to know what violet light, blue light, red light????

[email protected] SG

speed is distance over time

tanjun SG

U can try drawing a velocity vs time graph to solve this problem.
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.

tanjun SG

Their similarity and differences?
Similarity: Speed

Differences: Wavelength, Frequency

absol SG

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...

the.owl SG

1st question: use the kinematics equation then can find lor.

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.