Dimensional Analysis Problems Quiz

1. A key rule for a physically meaningful equation is that:

It must use only base units

Both sides must have the same dimensions

It must include π

It must avoid prefixes

Concept: dimensional consistency. Units on both sides must match for an equation to be valid. This is true regardless of the numbers used.

Explanation

Concept: dimensional consistency. Units on both sides must match for an equation to be valid. This is true regardless of the numbers used.

2. If two quantities have the same dimensions, they must represent the same physical concept.

True

False

Concept: same dimensions, different quantities. Different quantities can share units (e.g., energy and torque both n·m). Units help, but context is still required.

Explanation

Concept: same dimensions, different quantities. Different quantities can share units (e.g., energy and torque both n·m). Units help, but context is still required.

3. Which unit reduces to kg/(m·s²)?

N

Pa

J

W

Concept: pascal base-unit form. pa = n/m² and n = kg·m/s². Dividing by m² gives kg/(m·s²).

Explanation

Concept: pascal base-unit form. pa = n/m² and n = kg·m/s². Dividing by m² gives kg/(m·s²).

4. The unit of power (w) in base units is kg·m²/s____.

Concept: watt in base units. w = j/s and j = kg·m²/s². Dividing by s yields kg·m²/s³.

Explanation

Concept: watt in base units. w = j/s and j = kg·m²/s². Dividing by s yields kg·m²/s³.

Submit

5. Which expression has the units of energy?

Pressure / volume

Force / distance

Force × distance

Power / time

Concept: energy recognition. Energy is work, and work is force times distance. That gives units n·m, i.e., joules.

Explanation

Concept: energy recognition. Energy is work, and work is force times distance. That gives units n·m, i.e., joules.

6. Pa·m³ has units of joules.

True

False

Concept: pressure–volume work. pa·m³ = (n/m²)·m³ = n·m = j. This is why pressure–volume terms often represent energy.

Explanation

Concept: pressure–volume work. pa·m³ = (n/m²)·m³ = n·m = j. This is why pressure–volume terms often represent energy.

7. Which unit is the same as kg·m/s²?

J

W

N

Pa

Concept: newton identification. Newton is the SI unit of force. It matches kg·m/s² exactly.

Explanation

Concept: newton identification. Newton is the SI unit of force. It matches kg·m/s² exactly.

8. Which unit corresponds to kg·m²/s²?

N

J

Pa

Hz

Concept: joule identification. Joule is energy. It reduces to kg·m²/s².

Explanation

Concept: joule identification. Joule is energy. It reduces to kg·m²/s².

9. Hz can be written as s⁻¹.

True

False

Concept: frequency units. Frequency is cycles per second. So Hz is simply inverse seconds.

Explanation

Concept: frequency units. Frequency is cycles per second. So Hz is simply inverse seconds.

10. If velocity is m/s, then momentum (mass × velocity) has units of ______.

Concept: momentum units from definition. Multiply kg by m/s and you get kg·m/s. This is also consistent with impulse units n·s.

Explanation

Concept: momentum units from definition. Multiply kg by m/s and you get kg·m/s. This is also consistent with impulse units n·s.

Submit

11. Which unit best matches 'energy per time'?

J

N

W

Pa

Concept: power definition. Power measures the rate of energy transfer. So energy per time is watts.

Explanation

Concept: power definition. Power measures the rate of energy transfer. So energy per time is watts.

12. Dimensional analysis can catch using metres when you should use square metres in an area calculation.

True

False

Concept: detecting exponent mistakes. Unit exponents carry essential information. If you accidentally use m instead of m², the dimensions won’t match.

Explanation

Concept: detecting exponent mistakes. Unit exponents carry essential information. If you accidentally use m instead of m², the dimensions won’t match.

13. The unit n·s is dimensionally the same as:

J

Kg·m/s

Pa

W

Concept: impulse–momentum equivalence. n·s = (kg·m/s²)·s = kg·m/s. That matches momentum units.

Explanation

Concept: impulse–momentum equivalence. n·s = (kg·m/s²)·s = kg·m/s. That matches momentum units.

14. A quantity with units m²/s is often a diffusion-like coefficient, because it suggests 'area per ______.'

Concept: interpreting composite units. m²/s indicates spreading over an area as time passes. This kind of unit appears in diffusion and similar transport processes.

Explanation

Concept: interpreting composite units. m²/s indicates spreading over an area as time passes. This kind of unit appears in diffusion and similar transport processes.

Submit

15. Which statement is correct?

W = n·m

J = n/s

W = j/s

Pa = n·m

Concept: correct unit relationships. Watt is joule per second. n·m is joule, not watt.

Explanation

Concept: correct unit relationships. Watt is joule per second. n·m is joule, not watt.

16. If an equation produces units of kg·m²/s³, the result is a power-like quantity.

True

False

Concept: recognising power dimensions. kg·m²/s³ is the base-unit form of watt. So that dimensional result indicates power.

Explanation

Concept: recognising power dimensions. kg·m²/s³ is the base-unit form of watt. So that dimensional result indicates power.

17. Which is dimensionally consistent for kinetic energy?

(mass) × (speed)

(mass) × (speed)³

(mass) × (speed)²

(mass) / (speed)²

Concept: energy scaling with speed. Speed squared has units m²/s², and multiplying by kg gives kg·m²/s² (joules). That matches energy dimensions.

Explanation

Concept: energy scaling with speed. Speed squared has units m²/s², and multiplying by kg gives kg·m²/s² (joules). That matches energy dimensions.

18. The pascal (pa) is the same as j/m____.

Concept: pressure as energy density. Since pa = n/m² and n = j/m, pa = (j/m)/m² = j/m³. This links pressure to energy density.

Explanation

Concept: pressure as energy density. Since pa = n/m² and n = j/m, pa = (j/m)/m² = j/m³. This links pressure to energy density.

Submit

19. Which quantity most naturally has units of s⁻¹?

Energy

Force

Frequency

Pressure

Concept: frequency dimensions. Frequency counts occurrences per unit time. That’s why it’s measured in s⁻¹.

Explanation

Concept: frequency dimensions. Frequency counts occurrences per unit time. That’s why it’s measured in s⁻¹.

20. Breaking a derived unit into base units is a reliable way to see what kind of physical quantity an expression represents.

True

False

Concept: interpreting by base units. Base units reveal the underlying dimensions (mass, length, time, current, etc.). This helps you interpret unfamiliar combinations and check equations.

Explanation

Concept: interpreting by base units. Base units reveal the underlying dimensions (mass, length, time, current, etc.). This helps you interpret unfamiliar combinations and check equations.