This chapter's a sadist. please see this question. A drop-forge hammer, of mass 1500kg, falls under gravity...
[From: ] [author: ] [Date: 12-09-04] [Hit: ]
You can say -S.For part b you solve it the same way but a = 0. (It should be pretty obvious that the support force equals the weight in that case.)Btw - no need to e-mail me. I check here more than e-mail and I added you as a contact so I will watch your questions. I appreciate that you dont just post the question from the book and copy someones answer.......
Lastly, the force the hammer exerts on the metal is the equal and opposite reaction to S. So same magnitude but opposite direction. You can say -S.
For part b you solve it the same way but a = 0. (It should be pretty obvious that the support force equals the weight in that case.)
Btw - no need to e-mail me. I check here more than e-mail and I added you as a contact so I will watch your questions. I appreciate that you don't just post the question from the book and copy someone's answer. You try to solve the problem yourself and are genuinely interested in understanding.
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"Force exerted by hammer on metal = weight – force acting on it in opposite direction (decelerating it)"
Not quite. The weight of the hammer, and the reaction force to its decelerating force act in the same direction (down). So you sum them to find the force.
Let's put it this way. When you hit something with a hammer, is the force on the object greater while striking or while it's just sitting on it? It's greater while striking because you add the forces.
The decelerating force must be upward. But that force is on the hammer, not the die. The die "feels" the reaction force (downward), so the forces sum, not subtract.
EDIT:
"the hammer would indeed have a net force of mg-m(1.5) on it in downward direction."
Since the hammer is accelerating upward, it must have a net force on it that is upward.
"but the metal ''feels'' the reaction only. the force the hammer feels from it is support force or normal reaction that will be maximum when hammer is at rest."
No. The force on the hammer will depend on the interaction. When the force is maximized, the acceleration of the hammer must also be maximized (since the mass isn't changing).
Because the problem states that the hammer is decelerating uniformly, we know that the force on the hammer (causing the deceleration) is constant until it stops. At the moment it stops, the force disappears. So the maximum is not when the hammer is at rest.
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