DSST Physical Sciences 3 ā Questions and Answers
Question 1: A wave has a frequency of 500 Hz and a wavelength of 0.68 m. What is its speed?
- 0.00136 m/s
- 73.5 m/s
- 340 m/s (Correct answer)
- 500 m/s
Correct answer: 340 m/s
Wave speed = frequency Ć wavelength = 500 Hz Ć 0.68 m = 340 m/s (speed of sound in air).
Question 2: What is the molar mass of NaCl?
- 23 g/mol
- 35.5 g/mol
- 58.5 g/mol (Correct answer)
- 74.5 g/mol
Correct answer: 58.5 g/mol
Molar mass of NaCl = Na (23 g/mol) + Cl (35.5 g/mol) = 58.5 g/mol.
Question 3: Which principle states that the buoyant force on an object equals the weight of the fluid displaced?
- Pascal's Principle
- Bernoulli's Principle
- Archimedes' Principle (Correct answer)
- Hooke's Law
Correct answer: Archimedes' Principle
Archimedes' Principle describes why objects float or sink based on displaced fluid weight.
Question 4: In a chemical reaction, if the activation energy is lowered by a catalyst, what happens to the reaction rate?
- It decreases
- It increases (Correct answer)
- It stays the same
- It becomes zero
Correct answer: It increases
Lowering activation energy allows more molecules to have sufficient energy to react, increasing the reaction rate.
Question 5: Which quantum number describes the shape of an atomic orbital?
- Principal quantum number (n)
- Angular momentum quantum number (l) (Correct answer)
- Magnetic quantum number (ml)
- Spin quantum number (ms)
Correct answer: Angular momentum quantum number (l)
The angular momentum quantum number (l) defines orbital shapes: 0=s, 1=p, 2=d, 3=f.
Question 6: What happens to electrical resistance when the temperature of a conductor increases?
- Resistance decreases
- Resistance increases (Correct answer)
- Resistance stays constant
- Resistance becomes zero
Correct answer: Resistance increases
In metallic conductors, increased temperature causes more atomic vibrations, impeding electron flow and raising resistance.
Question 7: Which of the following is an example of a physical change?
- Burning wood
- Rusting iron
- Dissolving salt in water (Correct answer)
- Baking bread
Correct answer: Dissolving salt in water
Dissolving salt in water is physical because the NaCl can be recovered by evaporation ā no new substance is formed.
DSST Physical Sciences 3
A wave has a frequency of 500 Hz and a wavelength of 0.68 m.
What is its speed?