1. A spring with a force constant of 600 N/m is used in a scale for weighing fish. What is the mass of a fish that stretches the spring 7.5 cm from its normal length? [2 marks] 2. What is the average force that is required to stop a 1000 kg car travelling at a velocity of 20 m/s [Right] in a distance of 1.5 m? [2 marks] 3. A horizontal force of 50 N is applied to a 2.0 kg trolley, initially at rest, and it moves a distance of 4.0 m along a level, frictionless track. The force then changes to 20 N and acts for an additional distance of 2.0 m. What is its final velocity? [3 marks]