Free NEET Physics practice
Units and Measurements: MCQs with Solutions
Before substituting numbers into a formula, check its dimensions and the precision of the measurements. These five original questions move from dimensional reasoning to unit conversion and uncertainty, so you can identify whether an error comes from physics or arithmetic.
5 original practice questions — not previous-year paper reproductions. No account required.
By NEET Ninja · Updated
Before you answer
- Dimensions describe the kind of quantity, not its numerical size. Every term added in a physical equation must have the same dimensions.
- Leading zeros do not count as significant figures. Trailing zeros after a decimal point indicate measured precision.
- For maximum uncertainty in products and powers, add fractional uncertainties multiplied by the magnitude of each power. Convert the result to a percentage only at the end.
Questions and worked answers
Choose an option before reading the answer. For a wrong answer, identify the step or concept that changed the result.
QUESTION 1
What are the dimensions of pressure?
- M L T⁻²
- M L⁻¹ T⁻²
- M L² T⁻²
- M⁰ L⁻¹ T⁻¹
Answer: B — M L⁻¹ T⁻²
Pressure is force divided by area. Force has dimensions M L T⁻² and area has dimensions L². Dividing gives M L⁻¹ T⁻². The dimensions M L T⁻² belong to force, while M L² T⁻² belong to energy; neither includes the required division by area.
QUESTION 2
How many significant figures are in the measured value 0.00450 m?
- 2
- 3
- 4
- 5
Answer: B — 3
The zeros before 4 locate the decimal point and do not indicate measurement precision. The digits 4 and 5 are significant, and the final zero after the decimal is also significant. Therefore 0.00450 m has three significant figures, not two.
QUESTION 3
A length is measured as 2.0 cm with a maximum uncertainty of 0.1 cm. What is its percentage uncertainty?
- 0.5%
- 2%
- 5%
- 10%
Answer: C — 5%
Percentage uncertainty is the absolute uncertainty divided by the measured value, multiplied by 100. Here it is (0.1 cm / 2.0 cm) × 100 = 5%. The units cancel. Dividing the measured value by the uncertainty would invert the required ratio.
QUESTION 4
For Q = x²/y, the maximum percentage uncertainties in x and y are 2% and 3%. What is the maximum percentage uncertainty in Q?
- 1%
- 5%
- 7%
- 12%
Answer: C — 7%
For a product or quotient of measured quantities, maximum fractional uncertainties add with the absolute values of the powers. Thus ΔQ/Q = 2Δx/x + Δy/y, giving 2 × 2% + 3% = 7%. The denominator does not make its uncertainty subtract.
QUESTION 5
Which value in SI units is equal to 72 km h⁻¹?
- 10 m s⁻¹
- 20 m s⁻¹
- 25 m s⁻¹
- 72 m s⁻¹
Answer: B — 20 m s⁻¹
Convert kilometres to metres and hours to seconds: 72 × 1000 / 3600 = 20 m s⁻¹. Equivalently multiply a speed in km h⁻¹ by 5/18. Multiplication by 18/5 performs the reverse conversion, from m s⁻¹ to km h⁻¹.
Study source and corrections
Use the matching chapter in NCERT Class XI Physics, Part I — Units and Measurements for the underlying concepts. These questions are written for NEET Ninja, not endorsed or supplied by NCERT or NTA.
Want saved progress and more practice? The full question bank requires an account; current free and paid limits are listed on the pricing page.