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Acceleration of an elevator with different lectures of the weighing scale (7068)
A person of mass 70 kg stands on a weighing scale in an elevator which is moving and observes different lectures on it. Determine the acceleration of the elevator and if it is moving up, down, accelereting, breaking or not moving if the values of the scale are: a) 66 kg, b) 74 kg and c) 70 kg.
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Types of forces: at a distance or through contact (4841)
Indicate which of these phenomena are produced by forces at a distance and which are produced by forces through contact:
a) The motion of a train due to magnetic levitation.
b) The deformation of a spring when you attach a weight on it.
c) The skidding of a car on a pool of water.
d) The formation of the aurora borealis.
e) The motion of a cupboard when you push it.
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Classifying into laws and theories
Classify the next examples as laws or theories, considering the definition of each one.
a) When the temperature rises, will be simpler to dissolve a solid into the water.
b) The global warming is due to the excessive emissions of carbon dioxide, and other gases, to the atmosphere and it is the cause of many changes in the climates of the Earth.
c) In a chemical reaction, the total mass of the initial substances is equal to the total mass of the final substances.
d) A chemical reaction implies that substances change their composition and they have to be converted from one to other different substances by the combination of their atoms.
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Lengthen of a spring when a force is applied (4843)
A spring has an elastic constant of 120 N/m. Calculate how much it will lengthen by if a force of 35 N is applied.
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Classification of bodies: rigid, elastic or plastic (4842)
Classify the following objects into rigid, plastic or elastic bodies:
a) The mechanism of a key of the computer keyboard.
b) Sunglasses.
c) A headband.
d) A steel fork.
e) The bristles of a toothbrush.
f) Bread dough.