A student uses the apparatus below to investigate the extension of a spring for different weights. She adds 4 weights and takes some recordings which are shown in the table.

1. (a) Complete the table by adding the missing values for the extension. Assume there were no errors in taking the measurement. 

(b) The student read that ‘the extension of the spring is proportional to the weight added’. Based on this idea, what would be the expected extension for a weight of 30 N?

(c) The extension of the spring is not always proportional to the weight added because of the limit of proportionality. Explain what the limit of proportionality is.

(d) Suggest a kind of instrument that uses the idea that a spring can extend proportionally?

The graph shows the results of an experiment done to investigate the relationship between the force and extension of a spring.

(a) The student made an error in taking the readings for this experiment. What was the error?

(b) Label the point on the graph where the spring reached its limit of proportionality.

(c) The spring used in a different experiment has a spring constant of 40 N/Kg. Use the correct equation from the equation sheet to calculate the extension of the spring when a weight of 80 N is added.