Qualification > Sciences
Physics CIE help
halosh92:
A post is driven into the ground by means of a blow from a pile-driver. The pile-driver falls
from rest from a height of 1.6 m above the top of the post.
(a) Show that the speed of the pile-driver just before it hits the post is 5.6 m s–1. (2 marks)
The post has mass 6 kg and the pile-driver has mass 78 kg. When the pile-driver hits the top
of the post, it is assumed that the there is no rebound and that both then move together with
the same speed.
(b) Find the speed of the pile-driver and the post immediately after the pile-driver has hit the
post. (3 marks)
The post is brought to rest by the action of a resistive force from the ground acting for 0.06 s. By modelling this force as constant throughout this time,
(c) find the magnitude of the resistive force, (4 marks)
(d) find, to 2 significant figures, the distance travelled by the post and the pile-driver before
they come to rest. (4 marks)
how to do part c and d?
astarmathsandphysics:
C) use F=ma
You need to find a, the deceleration
When the driver hits the post momentum is conserved
v(6+78)=6*5.6 so v=33.6/84=0.4
post comes to rest in 0.06s
so a=(v-u)/t=0.4/0.06=6.66m/s^2
F=ma=84*6.66667=560N
d)use v^2=u^2+2as
0=0.4^2+2*-6.66667*s
s=0.16/13.33333=0.012m
*Hope*:
--- Quote from: ~ A.F ~ on April 23, 2010, 11:58:14 am ---Q20: W acts downward on X..therefore its tension..now its A or B
Also, any particle at point Y is pulled downwards, and therefore its under tension(this situation is exactly like the one where steel is beneath the concrete and weight is added..)
Q23: Actually this is A2 physics..lol but nvm :P..
You see..there are rules to memorize (and understand in A2):
* when there is maximum displacement, there is maximum acceleration and zero velocity..I magine a pendul swinging, at the far end there's maximum displacement, right? and also it momentarily stops, as it will move in the opposite direc. next---->therefore, max disp, max acc, zer velocity..
Also a pendulum swing exactly in the midpoint, will have its maximum velocity, where it has zero displacement (at the centre poiny of the system)
Therefore, in this case, point S has max displacement (on crest-amplitude) and so max acceleration..
Q27: You must exclude B and C at first..All arrows in each case point in the same direction, right? whislt a longitudinal wave is one in which compressions and rarefactions occur along the pathway of the wave...
So now its A and D...Again u must exclude D as arrows are pointing in the opposite direct, but this time AWAY from each other..There wouldnt be a wave then, as there wouldnt be a compression(no "squeazing" lol) ..and in D the particles would move AWAY from each other..
So the answer is A....
Q40:
You cudnt just depend on the mass alone..Its totally wrong..U must use the following equations:
E=qV...where q=charge, V= voltage
at the same time, E= 0.5 x m x v^2...right? Kinetic Energy..
therefore:
qV=0.5 m v^2
v^2= 2qV/m
however, Voltage V is constant..therefore:
v^2 is proportional 2 2q/m
Now u HAVE to substitute values in A, B, C, and D:
A---> m=1. q-1, therefore v= 2q/m
B---> m=4, q=2, therefore v= 2 x 2q/4m= q/m
C---> m=7, q=3, therefore v= 2qx3/7m= 6q/7m
D---> m=9, q=4, therefore v=2x4q/9= 8q/9m
C has the smallest ratio, and so C is the answer..
Tala! lol :P
Was I clear in everything? ::)
--- End quote ---
from where did u get "E=qV...where q=charge, V= voltage"?
~ A.F ~:
--- Quote from: lolo93 on April 24, 2010, 04:25:38 pm ---from where did u get "E=qV...where q=charge, V= voltage"?
--- End quote ---
from my physics book :P lol
its a general well-known rule
*Hope*:
LOL :D
but is E energy?
and also for q27, isn't it A and not B cuz the waves interfere in opp direction?
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version