An electric sewing machine moves a needle up and down. During one period of operation, the machine is supplied with 100 J of energy and transfers 60 J usefully to the moving needle. The drive mechanism becomes warm.
A student says that dissipated energy no longer exists.
State why this statement is incorrect.
Oil is added between the moving parts of the drive mechanism.
Give the force between the moving parts that the oil reduces.
Calculate the efficiency of the sewing machine.
Use:
η=EusefulEtotal \eta=\frac{E_{\text{useful}}}{E_{\text{total}}} η=EtotalEuseful100 exam-style questions on Edexcel GCSE Physics 3.2 Dissipation and efficiency, covering 3.2.1 Dissipation of energy, 3.2.2 Reducing unwanted energy transfers, 3.2.3 Efficiency, and 3.2.4 Increasing efficiency. Each one has a worked solution and a mark scheme showing where the marks go.