Physics and Science - Brain Easer

Difficulty - Medium, Interview Brain Teasers, Physics and Science

Throwing Rocks Off a Boat

A man is throwing rocks off a boat floating in the middle of a lake. The rocks sink quickly to the bottom of the lake.

Does the water level in the lake rise, fall, or stay the same after the rocks are thrown off the boat and sink to the bottom of the lake?

This question was asked in an actual mechanical engineering interview.

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Hint

Consider Archimedes’ principle and how the rocks affect the water level while they are on the boat vs. how the rocks affect the water level when they are in the lake.

Difficulty - Easy, Physics and Science

Two kids are playing around with their drinks at lunch. One has 200ml of milk and the other has 200ml of chocolate milk. They scoop 20ml of chocolate milk into the milk glass, then they scoop 20ml of whatever is in the milk glass into the chocolate milk glass.

When they’re done, is there more chocolate milk in the milk glass or more milk in the chocolate milk glass?

Difficulty - Easy, Physics and Science

Pulley Puzzle

In the pulley puzzle diagram below, there is a pulley attached to a scale. One side of the pulley is attached to a weight and the other side is attached to the ground.

If the scale reads 100g, does the weight weigh 50g, 100g, or 200g?

Assume the pulley and rope has no weight (the scale is already adjusted to account for these), and that the whole system is in equilibrium (nothing is moving).

Note: this puzzle is best solved with a bit of basic physics knowledge, but there is also an intuitive solution, so give it a shot.

Difficulty - Easy, Physics and Science

Balloon Direction Puzzle

You are driving your niece to a birthday party, and she is bringing a floating balloon filled with helium. When you make a sharp left turn, you both shift to the right. Which way does the balloon shift? Assume the windows are closed.

Difficulty - Easy, Physics and Science

Throwing a Ball

When you throw a ball straight up, does it spend more time going up, more time coming down, or the same time going up and down – taking into account both gravity and air resistance?

Difficulty - Medium, Interview Brain Teasers, Physics and Science

Burning Ropes

You have two lengths of rope that take exactly 60 minutes to burn. The ropes burn unevenly so if you cut the rope in half, burning a half will not necessarily take 30 minutes.

How do you precisely measure 45 minutes using these two ropes?