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Consider the three forces acting at O and in equilibrium as shown in the figure....

Physics
JAMB 2020

Consider the three forces acting at O and in equilibrium as shown in the figure. Which of the following equations is/are CORRECT?

I. P\(_1\) cos \(\theta_1\) = p\(_1\) cos \(\theta_2\)

II. P\(_3\) = P\(_1\) cos \(\theta_4\)  + P\(_2 cos_2\)

III. P\(_1 \sin \theta_1 = P_2 \sin \theta_2\)

  • A. I only
  • B. II only
  • C. III only
  • D. I, II and III only
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Correct Answer: Option C
Explanation

resolving \(P_1\), \(P_2\) and \(P_3\) into x and y component 

\(P_x\) = \(P_1 Cos\theta_1\)

\(P_y\) = \(P_1Sin\theta_1\)

\(P_x\) = \(P_2Cos\theta_2\)

\(P_y\) = \(-P_2Sin \theta_2\)

\(P_x\) = \(- P_3Cos \theta0\)

therefore 

total \(P_x\) = \(P_1 Cos\theta_1\) + \(P_2Cos \theta_2\) +  \(- P_3Cos \theta0\) = 0

total \(P_y\) = \(P_1Sin\theta_1\) +  \(-P_2Sin \theta_2\) = 0

so that   \(P_1Sin\theta_1\) =   \(P_2Sin \theta_2\)

\( P_3Cos \theta0\) =  \(P_1 Cos\theta_1\) + \(P_2Cos \theta_2\)

 

There is an explanation video available below.


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Explanation Video

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WAEC offline past questions - with all answers and explanations in one app - Download for free
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
WAEC offline past questions - with all answers and explanations in one app - Download for free