Help finding zeros of equation with trig function

  • Thread starter eHoaX
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1. Homework Statement

I need to find the times when the velocity is 0.
I am having difficulties finding multiple values for t.

v(t)=0

2. Homework Equations

v(t)=-40/3*cos(3/2*t)-5.129

3. The Attempt at a Solution
Attempt at solution:

v(t)=-40/3*cos(3/2*t)-5.129

V(t)=0

0=-40/3*cos(3/2*t)-5.129

cos(3/2*t)=-5.129*3/40

3/2*t=arccos(-5.129*3/40)

t=2/3*arccos(-5.129*3/40)

t=1.31

now I am not able to find the other values of t, I tried adding pi/2 but it didn't work

(it should be in radians)
 
Last edited:

Answers and Replies

  • #2
phinds
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Just as a suggestoin, "help" is not a subject line that is going to draw people who have an interest in the particular KIND of help you need.

Also, you need to read the forum rules. There's a template you should be using for homework problems.
 
  • #3
gneill
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Hi eHoaX. Welcome to Physics Forums.

As phinds mentioned, use the posting template provided when you begin a new thread in the homework sections. Also choose an threat title that describes the subject matter of your question; "Help" does not describe the topic or content, and one-word titles are almost never descriptive and are disallowed in general.

I will change the thread title to: Help finding zeros of equation with trig function.

I have also deleted your duplicate of this thread (which had no responses yet), although the title was much better :smile:

See the posting guidelines in the pinned thread, "Guidelines for students and helpers", at the top of the list of threads in the homework sections.
 
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  • #4
Student100
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1. Homework Statement

I need to find the times when the velocity is 0.
I am having difficulties finding multiple values for t.

v(t)=0

2. Homework Equations

v(t)=-40/3*cos(3/2*t)-5.129

3. The Attempt at a Solution
Attempt at solution:

v(t)=-40/3*cos(3/2*t)-5.129

V(t)=0

0=-40/3*cos(3/2*t)-5.129

cos(3/2*t)=-5.129*3/40

3/2*t=arccos(-5.129*3/40)

t=2/3*arccos(-5.129*3/40)

t=1.31

now I am not able to find the other values of t, I tried adding pi/2 but it didn't work

(it should be in radians)
Have you tried -2pin and + 2pin, there should be infinite times when velocity is zero.
 

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