JAMB Physics 2019 Objective — Question 5

Question 5 of 40 from the Joint Admissions and Matriculation Board (JAMB) Physics 2019 Objective paper, with the correct answer and a full explanation.

Two forces X and Y act on an object. The angle between the forces is 30°. Given that the magnitude of X is 15N while that of the resultant is 18N, what is Y?

A. 3.375NCorrect
B. 4.47N
C. 2.0142N
D. 5.59N

Explanation

Using the cosine rule with the supplementary angle (150°) between X and Y in the force triangle: 18²=15²+Y²−2(15)(Y)cos150° ⇒ Y²+25.98Y−99=0. Solving the quadratic gives Y=3.375N (taking the positive root).

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