Force and Laws of Motion

[muskan]

 

 

 

 

 

 

Answer this question please

[pzkpfw]

Did you read the sticky?

 

http://www.scienceforums.net/topic/75772-read-this-before-posting-in-homework-help/

[Klaynos]

What have you done to try and answer this?

[swansont]

Answer this question please

 

!

Moderator Note

That's not how the homework section works. You have to have made an effort and show what you have done. This is "homework help", not "someone else does you homework for you"

[muskan]

 

 

But this is not right.

 

 

 

[studiot]

It is a good idea to state the reason for each line in your working so that both the reason and the working can be checked on review.

 

You have assumed constant acceleration along the 12m trajectory.

 

Do you think this is correct?

 

What are the vectors?

 

Have you thought about resolving them vertically and horizontally?

 

Is the acceleration constant vertically and horizontally or should they be treated separately?

 

Have you thought about the work-energy theorem and equating PE, KE and work?

Edited March 2, 2017 by studiot

[Nicholas Kang]

Well, this question is basically about mechanics, work and energy. There is no need to use suvat in this case. Strategy:

Height already given-Hint: gravitational potential energy

Speed given-Hint: kinetic energy

Ok, apply principle of conservation of energy at both A and B

Assume you already know the basic knowledge: E_K = 0.5mv² , E_P = mgh,

Assume g=10 ms^-2 and let F_c = Frictional force, then

E_K at A + E_P at A = E_K at B + E_P at B + Word done against friction

3(10)(6) + 0.5(3)(4)² = (3)(10)(2) + 0.5(3)(8)² + F_c(12)

So, solve for F_c , you get F_c = 4N

That is the frictional force is 4N.

 

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Now, again using the same concept, we can find how far will the block be when it stops, hint: final energy= Energy required to counteract frictional force.

Ok,

Total energy at B= total energy at A + work done against friction from A to B = total energy done to do work against friction when the block has stopped

3(10)(6) + 0.5(3)(4)² = 4(Distance)

Total distance traveled by the block until it stops = 204/4

= 51 meter

But this distance include the distance from A to B, which is 12 m.

So, distance traveled from point B to the point where it has stopped is (51-12)m or 39 m.

OR

If you choose to start from point B, then

(3)(10)(2) + 0.5(3)(8)² = 4(Distance)

Distance = (60 + 96)/4

=39 m, which is the same answer as above.

 

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Remember, more practice is essential to develop an instinct that helps you solve Physics problems rapidly. But make sure you master the theories first before you begin.

Good luck with you studies!

Edited March 2, 2017 by Nicholas Kang

[studiot]

Since Nick has (against the rules) completed your homework for you, try o learn something from this.

 

Nick has made an unstated assumption in his solution to the second part:

 

Can you say what this is and why it is important?