What is the number one and most important rule to remember in soccer?

Astudent pushes on a 20.0 kg box with a force of 50 n at an angle of 30° below the horizontal. the box accelerates at a rate of 0.5 m/s2 across a horizontal floor. what is the value of the normal force on the box? 200 n 243 n 156 n 225 n

Can anybody me with this? ? (picture included.)

In the first law of thermodynamics, triangle e=q-w, what does q stand for