11th grade science

Example

Two students explain why a ball rolling on a flat floor eventually stops. Student 1: Objects naturally slow down and stop when nothing keeps pushing them. Student 2: Friction and air resistance act against the motion; with no resistive forces, the ball would keep moving at a steady speed. Which student's view agrees with Newton's first law?

1. Newton's first law: an object keeps moving at constant velocity unless a resultant force acts.
2. So the answer is: Student 2

Answer: Student 2

Example

Which stage of photosynthesis: fixes carbon dioxide with the enzyme RuBisCO?

1. The Calvin cycle in the stroma fixes carbon dioxide using ATP and NADPH to make sugars.
2. So the answer is: Calvin cycle (light-independent)

Answer: Calvin cycle (light-independent)

Example

After a first infection, a person's antibody level peaked at 25 arbitrary units after 12 days. After a second infection with the same pathogen it peaked at 250 units after 4 days. How many times higher was the second peak?

1. 250 ÷ 25 = 10
2. So the answer is: 10

Answer: 10

Example

A population of yeast cells (thousands per cm³) was counted each day: 15, 30, 60, 114, 186, 246, 285, 300, 297. Which value is closest to the carrying capacity?

1. The population stops growing at about 300.
2. So the answer is: 300

Answer: 300

Example

How much energy is needed to boil away 2 kg of water at 100 °C, in kJ? (Specific latent heat of vaporisation of water = 2260 kJ/kg)

1. 2 × 2260 = 4520
2. So the answer is: 4520 kJ

Answer: 4520 kJ

Example

A wire 0.05 m long carrying 5 A sits at right angles to a magnetic field of 0.5 T. What is the force on the wire, in N?

1. 0.5 × 5 × 0.05 = 0.125
2. So the answer is: 0.125 N

Answer: 0.125 N

Example

A piece of ancient wood has 50 % of the carbon-14 found in living wood. The half-life of carbon-14 is 5730 years. How old is the wood, in years?

1. 100 → 50 %: 1 half-lives
2. 1 × 5730 = 5730
3. So the answer is: 5730

Answer: 5730

Example

Annual mean CO₂ at the Mauna Loa observatory was about 317 ppm in 1960 and about 414 ppm in 2020. What was the mean rate of increase, in ppm per year? Give 1 decimal place.

1. (414 − 317) ÷ (2020 − 1960) = 97 ÷ 60 = 1.62
2. So the answer is: 1.6

Answer: 1.6

Example

About how old is the universe?

1. Measurements of the CMB and expansion give an age of about 13.8 billion years.
2. So the answer is: about 13.8 billion years

Answer: about 13.8 billion years

Example

A polar weather satellite orbits at a radius of about 7200 km from Earth's centre, taking 101 minutes per orbit. What is its orbital speed, in km/s? (v = 2πr ÷ T; give 1 decimal place)

1. T = 101 × 60 = 6060 s
2. 2π × 7200 = 45239 km
3. 45239 ÷ 6060 = 7.47
4. So the answer is: 7.5 km/s

Answer: 7.5 km/s