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*]

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 ..

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

Was I clear in everything?

from where did u get "E=qV...where q=charge, V= voltage"?

[~ A.F ~]

from where did u get "E=qV...where q=charge, V= voltage"?

from my physics book lol

its a general well-known rule

[*Hope*]

LOL
but is E energy?
and also for q27, isn't it A and not B cuz the waves interfere in opp direction?

[nid404]

ohk...E=qv  I'll tell u the derivation

energy= force X displacement right?

E=Voltage / distance & also E= Force/charge (E=Electric field strength)  [i hope ur aware of this one]

so Voltage / distance= Force/charge
   Force= Voltage X Charge / distance
   Energy= Force X displacement
            = Vq/ d  X d
             = Vq

Got it?

[tmisterr]

A cyclist is capable of an average output power of 3kw during a 4km speed trial. his aero dynamic suit and position reduce resistance forces to 180 newton. what is the approx time achieved in this time trial? been bugging me for 20 min

[student]

P=W/T
T=W/P
W=F*d
T=F*d/P
T=180*4000/3000=240s

[nid404]

thanks student

[tmisterr]

Ah thanks student! i was going to outerspace wit my solution

[*Hope*]

ohk...E=qv  I'll tell u the derivation

energy= force X displacement right?

E=Voltage / distance & also E= Force/charge (E=Electric field strength)  [i hope ur aware of this one]

so Voltage / distance= Force/charge
   Force= Voltage X Charge / distance
   Energy= Force X displacement
            = Vq/ d  X d
             = Vq

Got it?

Thanks but is electric field strength the same as energy??

[nid404]

Thanks but is electric field strength the same as energy??

noooooo!

[T.Q]

Thanks but is electric field strength the same as energy??

electric field: is a property that describes the space that surrounds electrically charged particles or that which is in the presence of a time-varying magnetic field. This electric field exerts a force on other electrically charged objects.

[astarmathsandphysics]

No electric field is more closely related to force via the equation F=Eq=Electric field*charge
but also W=Fd=Force *distance=Eqd

[*Hope*]

No electric field is more closely related to force via the equation F=Eq=Electric field*charge
but also W=Fd=Force *distance=Eqd

ok i get this one but for energy=VQ i am still confused since Energy is not = to electric field strength so we can not substitute there right??