Solving for Final Velocity Using Impulse Momentum Theorem - Homework Help"

[mpittma1]

Homework Statement

https://scontent-a-sjc.xx.fbcdn.net/hphotos-prn2/t1.0-9/10167935_1403417599934459_6123061969742894932_n.jpg

Homework Equations

The Attempt at a Solution

I used ∫Fdt = m(vf-vo)

and came up with -.822 m/s for the final velocity...

I have been reworking this problem over and over and cannot come up with a different answer...

Am i wrong in using the impulse momentum theorem?

 

[SammyS]

Homework Statement

https://scontent-a-sjc.xx.fbcdn.net/hphotos-prn2/t1.0-9/10167935_1403417599934459_6123061969742894932_n.jpg

Homework Equations

The Attempt at a Solution

I used ∫Fdt = m(vf-vo)

and came up with -.822 m/s for the final velocity...

I have been reworking this problem over and over and cannot come up with a different answer...

Am i wrong in using the impulse momentum theorem?

You haven't given any details regarding how you came up with -.822 m/s for the final velocity.

Why are you trying to find the final velocity anyway ?

 

[Andrew Mason]

Homework Statement

https://scontent-a-sjc.xx.fbcdn.net/hphotos-prn2/t1.0-9/10167935_1403417599934459_6123061969742894932_n.jpg

Homework Equations

The Attempt at a Solution

I used ∫Fdt = m(vf-vo)

and came up with -.822 m/s for the final velocity...

I have been reworking this problem over and over and cannot come up with a different answer...

Am i wrong in using the impulse momentum theorem?

Your approach is correct. Can you show us how you integrated? What is the anti-derivative of sin(ωt)?

AM

 

[mpittma1]

Your approach is correct. Can you show us how you integrated? What is the anti-derivative of sin(ωt)?

AM

sorry, should have done that from the get go, here is what i did: this is for when t = .55 seconds btw

https://scontent-a-sjc.xx.fbcdn.net/hphotos-prn2/t1.0-9/10001366_1403433926599493_210320460460652531_n.jpg

 

[mpittma1]

You haven't given any details regarding how you came up with -.822 m/s for the final velocity.

Why are you trying to find the final velocity anyway ?

Im not trying to find the final velocity but the velocity at time = .55 seconds

 

[Andrew Mason]

sorry, should have done that from the get go, here is what i did: this is for when t = .55 seconds btw

https://scontent-a-sjc.xx.fbcdn.net/hphotos-prn2/t1.0-9/10001366_1403433926599493_210320460460652531_n.jpg

Your integral is correct. I can't tell from your answer how you got the 9e-5 value but it is not correct. The given answer is correct. Remember the argument for cos(ωt) is in radians, not degrees.

According to your equation:

v_f = (1/m)∫Fdt + v₀

If you work that out you will get the answer that is given.

AM

 

[mpittma1]

Your integral is correct. I can't tell from your answer how you got the 9e-5 value but it is not correct. The given answer is correct.

According to your equation:

v_f = (1/m)∫Fdt + v₀

If you work that out you will get the answer that is given.

AM

Worked it out still got v(.55) = -.812 m/s

the answer is suppose to be v(.55) = -.451 m/s

 

[SammyS]

Worked it out still got v(.55) = -.812 m/s

the answer is suppose to be v(.55) = -.451 m/s

As AM said, ωt is in radians .

Your result looks like your calculator is in degree mode.

 

[mpittma1]

As AM said, ωt is in radians .

Your result looks like your calculator is in degree mode.

Hahaha thanks guys