All 10 questions from the Post-UTME Screening (Post-UTME) Physics 2010 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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The amount of energy released when 0.5kg of uranium is burnt completely is
Using E=mc² with c=3×10⁸m/s: E=0.5×(3×10⁸)²=0.5×9×10¹⁶=4.5×10¹⁶J. The exponents in the scanned options did not fully match this figure, so the precise lettered answer could not be confirmed from the source.
A body of mass 50kg slides down freely in a frictionless plane which is inclined at an angle of 30° to the horizontal. What force is pushing the body down the incline?
Force = mg sinθ = 50×9.8×sin30° = 245N.
A barometer can be used in determining the length of a: I. mountain II. Depth of a mine III. Dew point. Which of the following is/are correct?
A barometer measures atmospheric pressure and can be used to estimate altitude/depth via pressure differences (I and II); the source's key marks 'III only' as correct, though physically a barometer does not measure dew point — this looks like a likely error in the original key.
Which of the following colours of surfaces will radiate heat energy?
The source key states 'White'; however, by standard physics (Kirchhoff's law of thermal radiation), black surfaces are actually the best absorbers and emitters of thermal radiation — this looks like a likely error in the original key.
Which of the following is true for the image formed by a convex mirror? I. The image is always virtual II. The image is always erect III. The image is never magnified IV. The image is magnified V. The focal length is negative
A convex mirror's image is always virtual, erect, and diminished (never magnified). The source key marks 'All five' as correct, but statements III and IV directly contradict each other, so this looks like a likely error in the original key.
22,000J of heat is required to raise the temperature of 1.5kg of paraffin from 20°C to 30°C. The specific heat capacity of paraffin is
Q=mcΔθ: c=22000/(1.5×10)≈1466.7 J/(kg·°C), matching option A once its likely missing decimal point is accounted for.
A ball of mass 0.5kg moving at 10ms⁻¹ collides with another ball of equal mass at rest. If the two balls move together after the impact, calculate their common velocity.
This is a perfectly inelastic collision: v=(m1u1+m2u2)/(m1+m2)=(0.5×10+0.5×0)/(0.5+0.5)=5m/s.
If the temperature of a small quantity of water in a closed container is gradually increased from 0°C to 40°C, then the density of the water within this range
Water has an anomalous density maximum at 4°C, so density should increase from 0-4°C and then decrease from 4-40°C (option A). The source key states 'increase gradually' (option C), which appears to be an error given water's well-known anomalous expansion.
One of the properties of gamma rays is that they are
Gamma rays are electromagnetic radiation and carry no electric charge.
A thin converging lens has a power of 4.0 diopters, determine its focal length
Focal length = 1/Power = 1/4.0 = 0.25m.
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