Physics: Post your doubts here!

[hela]

for first question
momentum is conserved no matter whether the collision is elastic or inelastic
both bodies have same mass "m"
total momentum before collision
mv+m(0) since the second body is at rest
since total momentum before collision equals total momentum after collision
i.e mv
let V2 be the velocity of these two bodies
we know v is the velocity of first mass
from momentum of conversation
mv=2mV2
V2=v/2
k.e
1/2*2m*V2^2
m(v/4)
so A is the correct answer

for second question
take velocity in the right as positive and velocity in left as negative
(note:question asks about change in momentum not total momentum)
change in momentum=mv-mu
=m(v-u)
=0.1(20-(-30) (as 100g equal 0.1kg)
=0.1*50
=5
so B is the correct answer

for third question
let mass of one body equal m
take velocity in the right as positive and velocity in left as negative u can take the other way round
mv+mu
m(v+u)
m(60+(-40)
20m
since total momentum before collision equals total momentum after collision
20m=2mu
u=10
so A is the correct answer

for the fourth question
using area under graph
it is a trapezium
area of trapezium
=1/2*(base1+base2) *h
=1/2*(6+12)*2
=18m
so C is the correct answer

for the fifth question
difference between elastic and inelastic collision is that k.e is conserved in elastic collision
meaning total k.e before collision equals total k.e after collision
(1/2*2m*u^2)+(1/2*mu^2)
we get 1.5mu^2 as k.e before collision it must equal the k.e after collision only option that satisfies this condiiton is A so correct option is A
there is really no need to denote one velocity positive and the other as negative since squarring the number would always result in a positive answer

for the sixth question

Kinetic energy of 1st trolley = ½mv² = ½ x 2 x 2² =4J
Momentum of 1st trolley = mv = 2 x 2 = 4kgm/s to the left
From The conservation of momentum, the 2nd trolley's momentum = 4kgm/s to the right.
Since the 2nd trolley's mass =1kg, its velocity is 4m/s.
Kinetic energy of 2nd trolley = ½ x 1 x 4² =8J
Total kinetic energy = 4+8=12J. Since this energy has been supplied by the spring, the answer is D.

thanks a lot it was very helpfull

would you plaese solve the remaining question 7 ,8,9,10.
thanks again

 

[hela]

please solve these 3 question

 

[Tkp]

which question of summer 2004?

13,16,25,31

 

[Abu mota]

help q8

s=1/2at^2
L is directly proportional to t^2
so if u halve t u will quarter L so the answer is 0.25L which is B

 

[hela]

13,16,25,31

thanks a lot can you solve these

 

[hela]

can you solve these

 

[Abu mota]

please solve these 3 question

7. idk really.
8. D, because it is a rule if two particles of the same mass collide elastically then they interchange their velocities.
9. C , because young modulus is the same as long as the material is the same, and since they are both steel so the young modulus wont change.
10. D, because I is inversely proportional to x^2 which means that from the equation I is directly proportional to a^2 , a^2 is inversely proprtional to x^2 which means a is inversely proprtional to x, so if we double x we halve the amplitude. 8/2= 4 which is D.

 

[Abu mota]

13,16,25,31

13. A, because you have to consider the weight of the ruler which is 50N as it is a uniform ruler it must act at 1.5 ( half 3) which is 0.5 from the pivot 0.5x50=1xW (clockwise moment=anti-clockwise moment) W=25N
16. B, as there is no loss of energy to the surroundings as heat as there is no air resistance, the total energy of the ball will be constant.
25. A, always when u do this question move in the opposite direction to the energy travel, u will find that if u moved this way P will move downwards but as Q is maximum it will stay stationary (also for ur information minimum point stays stationary as well)
31.D, R is inversely proportional to d^2 so if u double d u will quarter the resistance at P, but as the question wants in terms of current then it will be 4 at P (as R is incersely proportional to current)

 

[Abu mota]

Hela:
for question 7 it might be because at first the total kinetic energy is 1/2 mv^2 and after that we have double the mass which mean kinetic energy is mv^2
as Ek= 1/2mv^2 then mv^2=2Ek then as we have two masses the kinetic energy is spread on both of them so 2Ek/2 will give Ek each and so there is no change in kinetic energy.
NOTE: imnot sure about the way i got the answer, i dont think it is correct.

 

[salvatore]

Aaaahhh, now i get it.. Thank you so muchh!! But what if we have constant velocity increase in a VELOCITY-TIME GRAPH, can we use the formula (a=v-u/t)?

Yeah.. that is possible. Ur welcome!

 

[Tkp]

13. A, because you have to consider the weight of the ruler which is 50N as it is a uniform ruler it must act at 1.5 ( half 3) which is 0.5 from the pivot 0.5x50=1xW (clockwise moment=anti-clockwise moment) W=25N
16. B, as there is no loss of energy to the surroundings as heat as there is no air resistance, the total energy of the ball will be constant.
25. A, always when u do this question move in the opposite direction to the energy travel, u will find that if u moved this way P will move downwards but as Q is maximum it will stay stationary (also for ur information minimum point stays stationary as well)
31.D, R is inversely proportional to d^2 so if u double d u will quarter the resistance at P, but as the question wants in terms of current then it will be 4 at P (as R is incersely proportional to current)[/quote
thanks fr the help bro but cn u explain 25 elaborately

 

[Tkp]

Hela:
for question 7 it might be because at first the total kinetic energy is 1/2 mv^2 and after that we have double the mass which mean kinetic energy is mv^2
as Ek= 1/2mv^2 then mv^2=2Ek then as we have two masses the kinetic energy is spread on both of them so 2Ek/2 will give Ek each and so there is no change in kinetic energy.
NOTE: imnot sure about the way i got the answer, i dont think it is correct.

..m1u1 + m2u2 = ( m1 + m2) v so Y is satationary so u = o so , mu/2m = v so v is 1/2 so the kinetic energy is also halfed so C

 

[littlecloud11]

OH BUddy ur great.nw i got it.ur really genius

Haha, Gracias. Happy to help

 

[Abu mota]

..m1u1 + m2u2 = ( m1 + m2) v so Y is satationary so u = o so , mu/2m = v so v is 1/2 so the kinetic energy is also halfed so C

no actually the answer is A for this question, i check the mark scheme.
anyway for Q.25 direction of energy travel is to the right so you move across the wave in the opposite direction which is to the left, then if u find that your finger goes down when u go across the wave at P, then it will move downwards. i find it very hard to explain how to answer the question, thats the best i can do.

 

[Tkp]

Haha, Gracias. Happy to help

ur frm which country?u have a cute avatar

 

[Tkp]

no actually the answer is A for this question, i check the mark scheme.
anyway for Q.25 direction of energy travel is to the right so you move across the wave in the opposite direction which is to the left, then if u find that your finger goes down when u go across the wave at P, then it will move downwards. i find it very hard to explain how to answer the question, thats the best i can do.

buddy the answer is c.check the markscheme carefully.we;; how the change in kinetic energy would be 0 for an inelastic collison?it should be c

 

[Abu mota]

buddy the answer is c.check the markscheme carefully.we;; how the change in kinetic energy would be 0 for an inelastic collison?it should be c

ok i think i saw a different mark scheme, it all makes sense now i tried to find an explanation for why it is A and i came up with a stupid explanation. ty for pointing it out.

 

[Tkp]

lol

 

[Tkp]

Haha, Gracias. Happy to help

cn u help me to solve mj 06 question 9.i face problems in this type of question.cn u draw it

 

[snowbrood]

cn u help me to solve mj 06 question 9.i face problems in this type of question.cn u draw it

Since it is a velocity - Time graph when the spring is at its lowest and highest position the speed will be equal to zero because it stops for a moment in time to switch direction. The velocity is highest while traveling through the equilibrium position. So the answer will be either b or d.
body first goes up reaches the maximum point and at that point is b and then the body goes down and on reaching minimum point that is D