Force and Motion
What force causes a bicycle to slow down when its brakes are applied?
Friction.
What type of energy does an object have because it is moving?
Kinetic energy.
Which of the following elements is classified as a metalloid?
A. Aluminum (Al)
B. Boron (B)
C. Gold (Au)
D. Carbon (C)
B. Boron (B)
Which of the following is an example of a physical change?
A. Burning a piece of wood
B. Rust forming on a bicycle
C. Cutting a sheet of paper into smaller pieces
D. Cooking an egg
C. Cutting a sheet of paper into smaller pieces
A book is resting on a desk. Gravity pulls the book downward, but the book does not move.
What force pushes upward on the book, balancing the force of gravity?
Normal force.
A runner travels 100 meters in 20 seconds. What is the runner's average speed?
5 m/s
A metal spoon is left sitting in a bowl of hot soup. After several minutes, the handle of the spoon becomes warm.
What method of thermal energy transfer caused the handle to become warm?
A. Radiation
B. Convection
C. Conduction
D. Evaporation
C. Conduction
An unknown element is shiny, malleable, and an excellent conductor of electricity.
Based on these properties, would the element most likely be classified as a metal, nonmetal, or metalloid?
Metal.
A student places an iron nail outside in the rain. After several days, a reddish-brown substance forms on its surface.
Is this a physical or chemical change?
Chemical change.
A passenger in a car suddenly moves forward when the driver slams on the brakes.
Which of Newton's three laws best explains why the passenger continues moving forward?
A. Newton's First Law
B. Newton's Second Law
C. Newton's Third Law
D. Law of Conservation of Energy
A. Newton's First Law
Objects in motion tend to remain in motion unless acted upon by an unbalanced force. This tendency is called inertia.
A student pulls a wagon to the right with a force of 60 N. Friction acts to the left with a force of 15 N. What is the net force acting on the wagon, and in which direction will it accelerate?
45 N to the right.
Net Force = 60 N − 15 N = 45 N
A student compares two identical containers of water. Container A is at 20°C, while Container B is at 80°C.
Which container has water particles with greater average kinetic energy, and why?
Container B.
The water in Container B has a higher temperature, meaning its particles have greater average kinetic energy.
The chemical formula for aluminum sulfate is Al₂(SO₄)₃.
How many oxygen atoms are present in one formula unit of aluminum sulfate?
12 oxygen atoms.
The subscript 4 indicates four oxygen atoms in each sulfate group. The subscript 3 outside the parentheses means there are three sulfate groups.
A student mixes two clear liquids in a laboratory. After mixing, the solution becomes cloudy, a solid forms, and the container becomes warmer.
Identify two pieces of evidence that suggest a chemical reaction occurred.
Formation of a solid (precipitate) and an increase in temperature.
Two students push a heavy box in opposite directions. Student A pushes with 80 N to the right, while Student B pushes with 55 N to the left.
What is the net force acting on the box, and in which direction will it accelerate?
25 N to the right.
Subtract the opposing forces:
80N - 55N = 25n
Because the net force is directed to the right, the box accelerates to the right.
A 15 kg box is pushed across the floor with a force of 60 N. Friction acts in the opposite direction with a force of 30 N.
What is the acceleration of the box?
2 m/s²
Step 1: Calculate net force.
60 N − 30 N = 30 N
Step 2: Calculate acceleration.
Acceleration = Net Force ÷ Mass
30 N ÷ 15 kg = 2 m/s²
A student switches on a battery-powered flashlight. The flashlight produces light, but after several minutes, the bulb also becomes warm.
Identify the sequence of energy transformations occurring in the flashlight.
Chemical energy → Electrical energy → Light energy + Thermal energy
The battery stores chemical energy, which is converted into electrical energy. The flashlight then converts electrical energy into light and thermal energy.
A scientist discovers an unknown element with the following properties:
It is brittle and breaks easily.
It has a dull appearance.
It is a poor conductor of electricity.
It is not malleable or ductile.
Based on these properties, how should the scientist classify the element?
A. Metal
B. Metalloid
C. Nonmetal
D. Rare Earth Metal
C. Nonmetal
A student performs three experiments:
Experiment 1: Ice melts into liquid water.
Experiment 2: A piece of magnesium burns and produces a white powder.
Experiment 3: Sugar dissolves completely in water.
Which experiment demonstrates a chemical change, and what evidence supports your answer?
Experiment 2 — Burning magnesium.
The formation of a new substance indicates a chemical change.
A swimmer pushes backward against the wall of a swimming pool and moves forward through the water.
Which of Newton's laws explains this motion, and how does it apply?
Newton's Third Law of Motion.
When the swimmer pushes backward against the wall, the wall pushes forward against the swimmer with an equal and opposite force, propelling the swimmer forward.
A 20 kg shopping cart is pushed forward with a force of 90 N. Friction opposes its motion with a force of 30 N. Using Newton's Second Law, calculate the cart's acceleration.
3 m/s²
Net Force = 90 − 30 = 60 N
Acceleration = Net Force ÷ Mass = 60 ÷ 20 = 3 m/s²
A heater warms the air near the floor of a room. After several minutes, warm air rises toward the ceiling while cooler air sinks toward the floor.
Identify the type of thermal energy transfer occurring.
Convection.
A scientist discovers an unknown element with the following properties:
It has a shiny, metallic appearance.
It is brittle rather than malleable.
It conducts electricity under certain conditions.
It is commonly used in electronic components.
Classify the element as a metal, nonmetal, or metalloid, and explain which properties support your answer.
Metalloid.
The element has characteristics of both metals and nonmetals.
A student places a piece of metal into a clear liquid. After several minutes, the student notices that bubbles are forming on the metal, the liquid has changed color, and the container feels warmer.
A classmate claims that only a physical change has occurred because the metal is still visible. Is the classmate correct? Explain your reasoning using at least two observations.
No, the classmate is incorrect. A chemical change has occurred.
Evidence includes:
Gas production: Bubbles suggest that a gas is being produced.
Color change: The liquid changing color may indicate that a new substance has formed.
Temperature change: The container becoming warmer suggests that energy is being released during the reaction.
A 25 kg crate is pushed to the right with a force of 120 N. Friction acts to the left with a force of 45 N.
Using Newton's Second Law, calculate the crate's acceleration.
3 m/s² to the right.