Page 17 - Q & A STPM 2022 Physics

Physics Semester 1 STPM Chapter 1 Physical Quantities and Units

Section B Structured Questions
Question 4

The diagram shows three coplanar forces acting on an object.
Penerbitan Pelangi Sdn Bhd. All Rights Reserved.
y

50 N

40 N 40° x
27°
Semester
1 60 N

Calculate the
(a) total vertical force, (c) resultant force,
(b) total horizontal force,
acting on the object.

Answer:
Exam Tips
y Exam Tips
50 sin 40° Forces in many different
50 N
directions can all be
40 N 40° 50 cos 40° x resolved into two directions
27° 60 cos 27° perpendicular to each other.
60 N

60 sin 27° Common Error
(a) Total vertical force Forces along +x-axis and +y-axis
= 50 sin 40° + (–60 sin 27°) are positive.
= 4.9 N Forces along –x-axis and –y-axis are
negative.
(b) Total horizontal force
= 50 cos 40° + 60 cos 27° – 40
Exam Tips
= 51.8 N Exam Tips

2
(c) F = 4.9 + 51.8 2 The resultant force is
4.9 N F = 52.0 N calculated from the triangle
θ 4.9 of forces using Pythagoras
51.8 N tan θ = 51.8 theorem.

θ = 5.4° above the horizontal
∴ the resultant force is 52.0 N, 5.4° with the horizontal

8

01 STPM Q&A PHY T1.indd 8 17/02/2022 10:03 AM