One way is the spinning of the wheels can be used to charge a battery. Just like with a generator, you can convert the rotational mechanical energy of the wheels spinning into electrical energy due to Faraday’s Law of Induction if there are magnets on the wheels.
As per Newton's II law we know that
here for the first case we know that
m = 3 kg
now we will have
now for other case we will have
m = 6 kg
now we have
The answer will be 50N.
This is because the spring reads weight and weight is mass times acceleration due to gravity.5kg*10m/s2=50N