1. A 20N block is being pushed across a horizontal table by an 18N force. If the coefficient of kinetic friction between the block and the table is 0.4, what is the acceleration of the block? (Could you also include a free body diagram and other relevant diagrams)?

2. When you walk, you push backwards on the Earth in order to propel yourself forward. However, according to their law, for every action, there is an equal and opposite reaction. How is it possible that you can move if this is the case? (This was a multiple choice and the answer given was - the mass of the earth is much larger than you and you push on the earth and the earth pushes on you.) I didn't understand why "the mass of the earth is much larger than you," is relevant for the answer.