Forces & elasticity

A student investigates a spring. They set up this apparatus.

Explain how the student finds the extension of the spring.

When the mass is removed, the spring returns to its original length.

This behaviour is called........

The student measures the extension of the spring for four different forces.

They plot a graph of force against extension.

Use any point on the graph to calculate the spring constant for this spring.

Use the equation: force exerted by a spring = spring constant × extension

Spring constant =........ N / m

Another student does the experiment. They use more forces.

Here is a graph of their results.

What extra information about the spring can be found from this graph?

Tick (✓) two boxes.

A spring has a spring constant of 20 N / m and its extension is 0.4 m.

What is the force exerted on the spring?

Use the equation: force exerted by a spring = extension × spring constant

A 0.8 N

B 5.0 N

C 8.0 N

D 20.4 N

A student stretches four different springs as shown in the table.

The student measures the length of each spring:

• before the stretching force is applied

• during the time that the stretching force is applied

• after the stretching force has been removed.

Which spring shows plastic deformation?

A spring has a spring constant of 20 N / m.

What is the extension of the spring when it is stretched by a force of 6 N?

The spring is not stretched beyond its limit of proportionality.

Use the equation: force exerted by a spring = spring constant × extension

A 0.3 m

B 0.3 mm

C 3.3 m

D 3.3 mm

9 0.18 J of energy is stored in a spring when it stretches by 12 cm.

What is the spring constant of the spring?

Use the Equation Sheet.

A 0.0025 N / m

B 3 N / m

C 12.5 N / m

D 25 N / m

The table shows the results from measuring the extension of a spring for different forces.

Calculate the spring constant of the spring.

Use the equation: force exerted by a spring = extension × spring constant

A 0.045 N / m

B 0.060 N / m

C 0.72 N / m

D 18 N / m

A 0.5 kg mass is placed on the end of a vertical spring with spring constant 125 N / m. The extension of the spring is 0.04 m.

What happens to the energy stored in the spring when a 1.0 kg mass is placed on the end instead?

Assume the spring obeys Hooke’s Law.

Use the Equation Sheet.

A Doubles

B Halves

C Quadruples

D Stays the same

Children often make models with clay. Clay and springs behave differently.

Draw three lines to match the materials to the properties.

Two children are squashing clay on a desk.

Child A says, ‘Only one force is needed to squash clay.’ Child B says, ‘There are three forces acting on the clay when I squash the clay.’

Using ideas about forces, explain why child B is correct.

Use a free-body force diagram to help explain your answer.

Fig. 12.1 shows a picture of a ball on a field. The ball is not moving.

Fig. 12.2 shows part of a free-body force diagram for the ball.

The force is drawn to scale. 1 cm = 1 N.

Complete the free-body force diagram by adding in the missing force.

Which word describes this missing force?

Contact Electrostatic Gravity Magnetic

A person kicks the ball.

Complete the sentences explaining what happens to the ball.

Choose words from the list.

You may use each word once, more than once or not at all.

balanced

forces

gravity

masses

speed

unbalanced

The........ on the ball are........

Therefore the........ of the ball changes.

The mass of the ball is 0.4 kg.

How much force is needed to accelerate the ball at 400 m / s²?

Use the equation: force = mass × acceleration

Fig. 12.3 shows the person placing the ball so it touches a wall.

He now kicks the ball directly at the wall.

The ball changes shape. Explain why.

A student carries out an experiment to calculate the spring constant of a spring.

Here are the student’s results.

Calculate the force when the mass is 200 g.

Use the equation: gravitational force = mass × gravitational field strength

Assume gravitational field strength = 10 N / kg.

Calculate the spring constant when the mass is 500 g.

Use the equation: force exerted by a spring = extension × spring constant

Give your answer to the nearest whole number.

Spring constant =........ N / m

Calculate the mean value of the spring constant.

Use the values in the table from 100 g to 400 g only.

Mean spring constant =........ N / m

The teacher says that calculating the mean is a poor method to find the spring constant, even though the student’s calculations are correct.

Describe a better way to find the spring constant using the student’s measurements.

A student hangs a mass from the end of a spring as shown in Fig. 13.1.

The spring in Fig. 13.1 extends by 0.06 m. The spring constant is 25 N / m.

Calculate the force on the spring.

Use the equation: force = extension spring constant

Label the forces on the diagram in Fig. 13.2.

The loop at the end of the spring breaks and the mass falls.

Explain why the mass falls and describe its motion as it falls.

The mass is placed on a bench, as shown in Fig. 13.3.

This is a diagram showing the force of the bench on the mass.

Newton’s third law is about how forces come in pairs.

Complete the table to describe the other force in this pair.

A student has two metal cubes, A and B, as shown in Fig. 12.1.

Each side of metal cube A is 1.0 cm. Each side of metal cube B is 2.0 cm.

Both metal cubes have the same mass. The density of metal cube A is 16 g / cm³.

Calculate the density of metal cube B.

Use the equation: density = mass ÷ volume

Density =........ g / cm³

Metal cube A sinks when placed in water.

Explain why.

The resultant force on the spring is zero.

Explain why.

Use your answer to 12(b)(i) to help you.

More than one force is required to stretch the spring.

Describe what happens if only one force is applied.

The student removes cube A and places another cube, cube C, on the spring.

The extension of the spring due to cube C is 0.04 m.

The spring constant of the spring is 30 N / m.

Calculate the weight of cube C.

Four springs A, B, C and D are made of four different materials.

Use the equation: Force = Extension × Spring constant

Which of the springs has the greatest spring constant?

A student measures the extension of a spring when it is stretched.

He hangs different cubes from the spring. He measures the extension of the spring for each cube.

Look at his results.

Plot a graph of the results on the grid.

Use the results and the graph to show the spring constant is 35 N / m.

The spring constant is 35 N / m.

Calculate the energy transferred to this spring when the extension is 0.2 m.

A student measures the extension of a spring when it is stretched.

He hangs different cubes from the spring. He measures the extension of the spring for each cube.

Look at his results.

Plot a graph of the results on the grid.

Use the results and the graph to show the spring constant is 35 N / m.

The spring constant is 35 N / m.

Calculate the energy transferred to this spring when the extension is 0.2 m.