All 10 questions from the Post-UTME Screening (Post-UTME) Physics 2008 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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A cone in an unstable equilibrium has its potential energy
An object in unstable equilibrium has its potential energy at a local maximum, so any disturbance increases (or rather, releases stored) potential energy as it topples.
A piece of rubber 10cm long stretches 6mm when a load of 100N is hung from it. What is the strain?
Strain = extension/original length = 0.6cm/10cm = 6×10⁻²; this value does not exactly match any listed option, which may reflect an OCR issue with the original choices.
An object of height 12.0cm is placed 240cm from a pinhole camera. If the image distance from the pinhole is 10.0cm, calculate the image height.
image height/object height = image distance/object distance: x/12=10/240, giving x=5cm.
Two resistors R1 and R2 are connected in parallel, R2 being greater than R1. The combined resistance is
For resistors in parallel, the combined resistance is always less than the smallest individual resistance, i.e. less than R1 (option A); the source key marks 'greater than R2' (option B), which appears to be a physics error.
A sonometer wire of length 100cm under a tension of 10N has a frequency of 250Hz. Keeping the length of the wire constant, the tension is adjusted to produce a new frequency of 350Hz. The new tension is
f∝√T, so T2=T1×(f2/f1)²=10×(350/250)²=19.6N.
A boy looks at the image of an object in a plane mirror. He observes two images, a main bright one and the other faint. The observed images result from
Per the source key, this is attributed to reflection only (from the front and back mirror surfaces); some textbooks instead attribute the faint secondary image to combined reflection and refraction at the glass surface, so this is worth double-checking against your syllabus.
One of the properties of gamma rays is that they are
Gamma rays are uncharged electromagnetic radiation.
The wavelength of the first overtone of a note in a closed pipe of length 33cm is
For a closed pipe, the first overtone (3rd harmonic) has wavelength 4L/3 = 4(33)/3 = 44cm (option A); the source key marks 33cm (option B), which appears to be an error.
A wire of length 15m made of a material of resistivity 1.8×10⁻⁶Ω·m has a resistance of 0.27Ω. Determine the area of the wire
A=ρL/R = (1.8×10⁻⁶×15)/0.27 ≈ 1.0×10⁻⁴m².
What is the number of neutrons in the uranium isotope ²³⁸U (Z=92)?
Neutrons = mass number - protons = 238-92 = 146.
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