Science Physical Science Flashcards

A 2 kg object moving at 6 m/s collides with a stationary 4 kg object. After the collision, both objects move together. What is their combined velocity?

Answer: 2 m/s

This is a perfectly inelastic collision. Using conservation of momentum: p_before = p_after. (2 kg × 6 m/s) + (4 kg × 0) = (2 + 4) kg × v. 12 kg·m/s = 6 kg × v, so v = 2 m/s.

Which of the following best explains why a pressure cooker cooks food faster than a regular pot with a lid?

Answer: Increased pressure raises the boiling point of water above 100°C

In a sealed pressure cooker, steam builds up and increases the internal pressure. According to the relationship between pressure and boiling point, higher pressure raises the boiling point of water above 100°C. This means the water — and steam — reaches a higher temperature, cooking food faster.

An atom of element X has 17 protons, 18 neutrons, and 18 electrons. Which statement about element X is correct?

Answer: It is a negatively charged ion with mass number 35

With 17 protons, this is chlorine (Cl). The mass number = protons + neutrons = 17 + 18 = 35. Because it has 18 electrons but only 17 protons, it has one extra electron, giving it a charge of −1. This makes it Cl⁻, a negatively charged chloride ion with mass number 35.

Two identical metal spheres, one charged at +8 μC and one at −2 μC, are touched together and then separated. What is the charge on each sphere after separation?

Answer: +3 μC each

When identical conductors touch, charge distributes equally between them. The total charge is +8 + (−2) = +6 μC. Dividing equally: each sphere gets +6 ÷ 2 = +3 μC.

A wave traveling through water has a frequency of 5 Hz and a wavelength of 3 meters. If the frequency is doubled while the medium stays the same, what happens to the wavelength?

Answer: It decreases to 1.5 meters

Wave speed (v = frequency × wavelength) is determined by the medium and remains constant. If frequency doubles from 5 Hz to 10 Hz and wave speed stays at 15 m/s, then wavelength = v ÷ f = 15 ÷ 10 = 1.5 meters. Frequency and wavelength have an inverse relationship at constant speed.

During electrolysis of water, oxygen gas is produced at one electrode and hydrogen gas at the other. The volume of hydrogen produced is always twice the volume of oxygen. Which explanation best accounts for this ratio?

Answer: The chemical formula of water (H₂O) requires 2 hydrogen atoms for every 1 oxygen atom, so twice as many hydrogen molecules are released

Water has the formula H₂O — two hydrogen atoms for every one oxygen atom. During electrolysis, the reaction 2H₂O → 2H₂ + O₂ shows that for every molecule of O₂ produced, two molecules of H₂ are released. Since equal volumes of gas at the same conditions contain equal numbers of molecules (Avogadro's law), hydrogen volume is exactly double that of oxygen.