Suppose we have two objects 1kg mass. The one of them moves by constant velocity 3m/s and then we apply to it force equals 1N so the done work is 3.5 joule. the other object is at rest and then apply to it force 1 N. so the work is 0.5 joule. this makes me feel by confusion because actually i did same work but the formula gives me different results.
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4$\begingroup$ Please explain how you got 3.5 and 0.5 joules. $\endgroup$– Not_EinsteinCommented Jan 27, 2020 at 19:19
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$\begingroup$ What formula(s) are you using? Is the 1N force applied to each the net force? You need to provide more details $\endgroup$– Bob DCommented Jan 27, 2020 at 20:12
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$\begingroup$ For first scenario W = 1 N * 3.5 m = 3.5 joule/ seconde W = 1 N * 0.5 = 0.5 joule $\endgroup$– user252640Commented Jan 27, 2020 at 21:30
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$\begingroup$ For first scenario W = 1 N * 3.5 m = 3.5 joule/ seconde W = 1 N * 0.5 = 0.5 joule $\endgroup$– user252640Commented Jan 27, 2020 at 21:30
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$\begingroup$ Is the slash separating the scenarios, or is the first scenario 3.5 J/s. Please clarify. $\endgroup$– Bob DCommented Jan 27, 2020 at 22:31
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1 Answer
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What does work really mean deeply?
At the most basic level, work is one of the two means by which energy can be transferred between objects. The other is heat.
In the case of work it is energy transfer due to a net force times a displacement. If the net force is in the same direction as the displacement, work is said to be positive, meaning energy is transferred to the object being displaced. If the net force is in the opposite direction as the displacement, work is said to be negative, meaning energy is taken from the object being displaced. An example of negative work is kinetic friction work. The kinetic friction force opposes the displacement of the object.
Heat, the other means of energy transfer, is energy transfer between objects due solely to a temperature difference between the objects.
In response to my questions on your post I understand your two scenarios as follows:
For the first scenario, the 1 kg mass is initially moving at a constant velocity of 3.5 m/s. This tells me that, initially, there is no net force acting on the mass. Then a 1 N force, which I assume is constant, is applied to the mass, presumably in the same direction as the initial velocity of the mass. Assuming the 1 N force is the net force acting on the object, then if you say 3.5 J of work is done on the object, the force had to act over a displacement of 3.5 m. The initial velocity is irrelevant in terms of the work done.
Likewise, for the second scenario, if 0.5 J of work is done on the mass, then the force had to act over a displacement of 0.5 m. The fact that the mass was initially at rest does not matter.
Bottom line: In both scenarios you are using the formula force x displacement, where the force and mass is the same. In one scenario you indicate the displacement is 3.5 m. In the other, you indicate the displacement is 0.5 m. That gives you 3.5 J of work for the first scenario and 0.5 J of work for the second.
The only other difference between the scenarios that in scenario 1 the mass has an initial velocity whereas in scenario 2 it starts at rest. Is that what's causing you confusion? If so, how and why?
Hope this helps.
