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Science 8

Science 8 · Worksheets

Year-end challenge

Ten questions of mixed difficulty, covering Cells and systems, Fresh and salt water, Light and optical systems, Mechanical systems, Mix and flow of matter. Print it, or work through it on screen — the answer key starts on its own page.

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Year-end challenge

Science 8 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. A pinhole camera is a box with a tiny hole in one end and a paper screen at the other. The image of a tree on the screen is upside down. Why?

    1. a) The whole image squeezes through the hole and turns over on the way
    2. b) Light reflects off the inside walls of the box before reaching the screen
    3. c) Rays travel straight, so light from the treetop lands at the bottom
    4. d) The pinhole acts like a lens, bending the light so that the image flips

  2. At most, 32 g of potassium nitrate dissolves in 100 mL of water at 20 °C, 64 g at 40 °C and 110 g at 60 °C. A saturated solution in 100 mL of water at 60 °C is cooled to 20 °C. About how much solid forms?

    1. a) 32 g
    2. b) 46 g
    3. c) 142 g
    4. d) 78 g

  3. In a hydraulic jack, the small piston has an area of 2 cm² and the large piston an area of 50 cm². The small piston is pushed down 10 cm. How far does the large piston rise?

    1. a) 0.4 cm
    2. b) 250 cm
    3. c) 10 cm
    4. d) 4 cm

  4. You step out of a dark movie theatre into bright sunlight, and your pupils shrink. Which part of the eye makes them smaller?

    1. a) The retina
    2. b) The lens
    3. c) The iris
    4. d) The cornea

  5. A river curves around a bend. On one side the bank is steep and wearing away; on the other, a sandy bar is building up. Where is the steep, eroding bank?

    1. a) On the outside of the bend, where the water flows fastest
    2. b) On the inside of the bend, where the water flows slowest
    3. c) On the inside of the bend, where the water flows fastest
    4. d) On the outside of the bend, where the water flows slowest

  6. Happy Valley-Goose Bay, in Labrador, and Dublin, in Ireland, are both about 53° north of the equator, yet Goose Bay's winters are far colder. Which ocean currents help explain this?

    1. a) The same warm current flows past both, cooling on the way
    2. b) A warm current reaches Ireland; a cold one flows past Labrador
    3. c) No currents; Ireland is simply closer to the equator
    4. d) A cold current reaches Ireland; a warm one flows past Labrador

  7. A student blocks the tips of two syringes, one full of air and one full of water, and pushes hard on each plunger. What happens?

    1. a) Both squeeze into about half of their space
    2. b) The water squeezes into less space; the air barely does
    3. c) Neither moves, since both tips are blocked
    4. d) The air squeezes into less space; the water barely does

  8. Some ancient thinkers believed the eye sends out rays that travel to an object, and that this is how we see it. Which observation is the strongest evidence against that idea?

    1. a) You cannot see anything in a completely dark room
    2. b) Two people can look at the same tree at once
    3. c) Objects far away look smaller than objects nearby
    4. d) Your eyes feel tired after a long time reading

  9. An amoeba is a single cell. A grizzly bear is made of trillions of cells. Which statement about them is true?

    1. a) The amoeba's one cell does every job; the bear's cells specialize
    2. b) The amoeba needs no food, because one cell uses so little energy
    3. c) Each of the bear's cells can do every job the whole bear does
    4. d) The amoeba is not really alive, because it is made of only one cell

  10. A student pushes a box 4.0 m up a ramp with a force of 250 N. The box, which weighs 600 N, rises 1.5 m. What is the ramp's efficiency?

    1. a) 42%
    2. b) 111%
    3. c) 90%
    4. d) 240%

Answer key · Year-end challenge

Science 8 · maddyhelps.com

  1. c) Rays travel straight, so light from the treetop lands at the bottom — Light from the top of the tree travels in a straight line down through the hole and lands at the bottom of the screen, while light from the bottom lands at the top, so the image is flipped. A pinhole has no glass and bends nothing; the image is built point by point from straight rays, not carried through the hole as a whole picture.
  2. d) 78 g — At 60 °C the water holds 110 g, but at 20 °C it can hold only 32 g, so 110 − 32 = 78 g comes out of solution as crystals. 32 g is what stays dissolved, not what comes out, and 46 g is the answer for cooling only to 40 °C.
  3. a) 0.4 cm — The oil pushed out of the small cylinder, 2 cm² × 10 cm = 20 cm³, must fit into the large cylinder, where it spreads over 50 cm², so the large piston rises 20 ÷ 50 = 0.4 cm. The large piston pushes with 25 times the force but moves only a twenty-fifth as far; multiplying by 25 instead gives 250 cm.
  4. c) The iris — The pupil is just an opening; the iris is the coloured ring of muscle around it, which narrows the pupil in bright light and widens it in dim light, as a camera's aperture does. The lens focuses the light, and the retina detects it.
  5. a) On the outside of the bend, where the water flows fastest — Water swings to the outside of a bend and flows fastest there, so it has the energy to cut into the bank. On the inside it slows down, and slow water drops the sand it was carrying, which is how a river's bends slowly grow and shift across a valley.
  6. b) A warm current reaches Ireland; a cold one flows past Labrador — The Gulf Stream and its extension, the North Atlantic Drift, carry warm water from the tropics across the Atlantic toward Ireland, while the cold Labrador Current flows south from the Arctic along Labrador's coast. Air over each coast takes on the warmth or chill of the water, so places at the same latitude can have very different winters.
  7. d) The air squeezes into less space; the water barely does — Gas particles are far apart, with empty space between them, so a push crowds them closer together; liquid particles are already touching, so water hardly compresses at all. That is why tires are filled with air, which cushions bumps, while hydraulic machines use liquids, which pass a push straight along.
  8. a) You cannot see anything in a completely dark room — If the eyes sent out their own rays, you could see in the dark with your eyes open. You cannot, because seeing needs light from a source that bounces off the object and into your eye; far objects looking small fits either idea, so it cannot decide between them.
  9. a) The amoeba's one cell does every job; the bear's cells specialize — A single-celled organism must take in food, get rid of wastes, move and reproduce, all within one cell. In a multicellular organism, cells specialize as muscle, nerve, blood and other cells and depend on each other, so one bear cell could not survive on its own.
  10. c) 90% — Input work = 250 N × 4.0 m = 1000 J and output work = 600 N × 1.5 m = 900 J, so efficiency = 900 ÷ 1000 × 100% = 90%. An answer over 100% means something is upside down: friction always turns some input work into heat, so no real machine gets out more work than goes in.