You push on a tree with 20 N of force. If the tree doesn't move, the tree is pushing back on you with of force.

according to the newton's third law of motion every action has a equal and opposite reaction.

so the answer would be reaction

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може ли да зареждате повече информация, моля

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.