Page 12 - Q & A STPM 2022 Physics

Physics Semester 1 STPM Chapter 1 Physical Quantities and Units
Question 2

Which of the following equations is homogeneous?
A T = 4π 2 l g where T = period, l = length, g = gravitational field strength
B E = ½ ρ v where E = energy, ρ = density, v = velocity
2
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C F = P/t where F = force, P = power, t = time
D E = PV where E = energy, P = pressure, V = volume

Answer: D Semester
–2
A [T] = T [l/g] = L/L T = T 2
B [E] = M L T –2 [ρv ] = M L L T = M L T –2
–3
2
–1
2
–2
2
2
C [F] = M L T –2 [P/t] = M L T / T = M L T –4 1
–3
2
2
2
3
D [E] = M L T –2 [PV] = M L T L = M L T –2
–1
–2
Exam Tips
Exam Tips
The equation is homogeneous when the dimensions in both sides of the
equation are equal.
Question 3
The force F between the two isolated point charges, Q separated with a distance
R is given by the equation
F = k Q R .
y
x
3
Where the unit for k is kg m A s . What are the values of x and y?
–2
–4
x y
A 1 1
B 1 –2
C –2 1
D 2 –2
Answer: D
–2
3
[F] = M L T –2 [Q]= A T [R] = L [k]= M L A T –4

–2
–2
3
M L T = (M L A T )(A T) L y
x
–4
= M L A –2+x T –4+x
3+y
Equating the coefficient
y : 1 = 3 + y y = –2
x : –2+ x = 0 x = 2 or –4 + x = –2 x = 2
3

01 STPM Q&A PHY T1.indd 3 17/02/2022 10:03 AM