Final answer:
The spring scale must show a reading equal to 20 N when lifting a 2 kg mass with constant velocity, as it has to balance out the gravitational force acting on the mass. Therefore, the correct option is 1.
Step-by-step explanation:
The question is related to Newton's second law of motion and the concept of forces acting on objects. When an object is lifted with a constant velocity, the net force acting on it must be zero because acceleration is zero (a = 0). In the case of lifting a 2 kg mass with a spring scale, the spring scale must balance the gravitational force acting on the mass. The gravitational force (weight, w) can be calculated using the equation w = mg, where m is the mass and g is the acceleration due to gravity (approximately 9.81 m/s2). Therefore, if the mass is 2 kg, the weight would be w = 2 kg × 9.81 m/s2 = 19.62 N, which we round to the nearest whole number as 20 N due to the context of the choices. Therefore, the reading on the spring scale must be equal to 20 N to lift the mass with constant velocity, indicating option 1) is the correct answer.