A spring is stretched 4 centimetres by a 20 newton force. According to Hooke's law, how far will it stretch under a 40 newton force, assuming it stays within its elastic limit?

Correct answer to question 200 (Mechanical Comprehension): 8 centimetres

Method

Hooke's law states extension is proportional to applied force within the elastic limit, so doubling the force doubles the stretch to 8 centimetres.