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akhl

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Posted: 11 November 2008 at 3:14am | IP Logged

The flowers shrivelled up due to excessive heat.

The detectives thrashed out in the meeting in order to find how the crime was committed.

Edited by akhl - 11 November 2008 at 3:21am

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rosha

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Posted: 11 November 2008 at 10:15am | IP Logged

Originally posted by akhl

The flowers shrivelled up due to excessive heat.

The detectives thrashed out in the meeting in order to find how the crime was committed.

thank you sooooooooooooooooo much ! Big smile

ashutosh_web

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Joined: 15 November 2008

Posts: 21

Posted: 16 November 2008 at 11:20am | IP Logged

im totaly inspired by the idea. well looking at u guys, i also want to do something.

So, if anybody have any query about IT or softwares can ask. u cud also feel free for PM me with ur queries. May be i wud also require help someday..... Day Dreaming

aishu_fan

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Joined: 21 May 2007

Posts: 2879

Posted: 16 November 2008 at 6:52pm | IP Logged

can someone PLZ plz PLZZZ plzzzzzzz help me with physics!?!!?

1. If the speed of a particle is doubled, by what factor is its momentum changed?

By what factor is its kinetic energy changed?

2. a pitcher claims he can throw a 0.145 kg baseball with as much momentum as a speeding bullet. assume that a 3.00 g bullet moves at a speed of 1.5 x 10^3 m/s

A.what must be the baseball's speed be of the pitcher's claim is valid.

b.which has greater kinetic energy,the ball or the bullet?

A 0.42 kg soccer ball is moving downfield with

a velocity of 12 m/s. A player kicks the ball so that it has a final velocity of

18 m/s downfield.

a. What is the change in the ball's momentum?

b. Find the constant force exerted by the player's foot on the ball if the

two are in contact for 0.020 s.

When a force is exerted on an object, does a large force always produce a

larger change in the object's momentum than a smaller force does? Explain.

5.What is the relationship between impulse and momentum?

akhl

IF-Rockerz

Joined: 30 March 2007

Posts: 5042

Posted: 16 November 2008 at 8:58pm | IP Logged

Hi aishu,

It will be good if together with the questions, you also show what you tried yourself. Then you will learn better. Anyway, since you asked, let me answer.

1. If speed is doubled, then momentum doubles.

Reason: Momentum = mass * velocity

Speed is magnitude of velocity. So if speed doubles, this means velocity doubles in magnitude and that means momentum doubles in magnitude.
If speed doubles, then kinetic energy becomes 4 times.

Reason: Kinetic energy = 1/2 M v^2

where M = mass, v = speed. As you can see, if v doubles, then v^2 becomes 2^2 i.e. 4 times. Therefore, kinetic energy becomes 4 times.

2. Mass of baseball M1 = 0.145 kg

Mass of bullet M2 = 3.00 g = 3.00 * 10^-3 kg

Speed of bullet v2 = 1.5 * 10^3 m/s

A. Speed of baseball v1 = ?

Momentum of baseball = momentum of bullet

Therefore M1 v1 = M2 v2

Or v1 = M2 v2/M1 = 3.00 * 10^-3 * 1.5 * 10^3/0.145 = 4.5/0.145 = 31.03 m/s

B. Kinetic enegry of baseball K1 = (1/2)M1 v1^2

Kinetic energy of bullet K2 = (1/2)M2 v2^2

M1 v1 = M2 v2

Squaring both sides,

M1^2 v1^2 = M2^2 v2^2

M1 * M1 v1^2 = M2 * M2 v2^2

M1 * 2 * (1/2) M1 v1^2 = M2 * 2 * (1/2) M2 v1^2

M1 * 2 K1 = M2 * 2 K2

Dividing by 2,

M1 * K1 = M2 * K2

K1/K2 = M2/M1

M2 < M1

Therefore K1 < K2

Therefore K2 i.e. kinetic energy of bullet is greater.

Ans: The bullet has greater kinetic energy.

3. Mass M = 0.42 kg

Initial velocity vi = 12 m/s downfield

Final velocity vf = 18 m/s downfield

a. Change in momentum = M(vf - vi)

= 0.42*(18 - 12)

= 0.42 * 6

= 2.52 kg-m/s downfield

Ans: 2.52 kg-m/s downfield

b. Time t = 0.020 s

Let F = force

F = change in momentum/time = 2.52/0.020 = 126 N downfield

4. Not necessary.

For a constant force, change in momentum = force * time

So force alone is not sufficient. Time also matters. If both forces act for equal time, then larger force will produce larger momentum. But if larger force acts for smaller time, then which will produce larger momentum depends on what the values of the forces are and for what time they act.

5. The impulse of a force acting on an object is equal to the change in momentum of the object caused by the force.

aishu_fan

IF-Dazzler

Joined: 21 May 2007

Posts: 2879

Posted: 16 November 2008 at 9:19pm | IP Logged

allah ya kilmak ya rab!

thnk u sooo sooosoo soo much!!! may u be happy in everything u do! THNKKKKKKKK U!!THNK THNK U!

aishu_fan

IF-Dazzler

Joined: 21 May 2007

Posts: 2879

Posted: 17 November 2008 at 8:10pm | IP Logged

its me once again, im so sorry for the bother but i really need help,u told me to try not just hope for the answer,believe me i tried!i just dont get it...? plzzzz help me!

1.44 kg student on in-line skates is playing with a 22 kg excercise ball. disregarding friction,explain what happens during the following situations.

A. the student is holding the ball and both are at rst. the student then throws the ball horizontally,causing the student to glide back at 3.5 m/s.

B. explain what happens to the ball in part (a) in terms of the momentum of the student and the momentum pf the ball

C.the student is initally at rest. the student then catches the ball,which is intitally moving to the right at 4.6 m/s.

D.explain what happens to in part(c) in terms of the momentum of the student and the momentum of the ball.

2. a boy stands at one end of a floating raft that is stationary relative to the shore. he then walks in a straight line to the opposite end of the raft,away from shore.

A. what is the total momentum of the boy and the raft before the boy walks across the raft.

B. what is the total momentum of the boy and the raft after the boy walks across the raft?

akhl

IF-Rockerz

Joined: 30 March 2007

Posts: 5042

Posted: 17 November 2008 at 8:51pm | IP Logged

1)You have put questions A,B,C,D. But it looks like A and B together make one question. Likewise, C and D together make one question. A is the situation and B is the question on that situation. C is the situation and D is the question on that situation. Let me know if it is correct.

And you have given mass of the student as 1.44 kg.

Are you sure that you typed correctly? 1.44 kg is too small.

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