Physics Review QuestionUnit:
mechanicsYear:
1996 Question#:
07Question:
A 4.0-kilogram rock and a 1.0-kilogram stone fall freely from rest from a height of
100. meters. After they fall for 2.0 seconds, the ratio of the rock's speed to the
stone's speed is(1
) 1:1(2
) 2:1(3
) 1:2(4
) 4:1What is this question really asking?
Explanation by: Christine A [ Return to question menu
]Answer 1
1:1 CORRECT Theoretically all objects should fall with an equal speed regardless of the object's weight or shape. However, in the Earth's atmosphere, air friction prevents this law from being completely true. Thus, a feather will fall to earth more slowly than would a pencil, due to the increased available surface area of a feather. Despite this, when we are given a question such as this, "FREE FALL" tells you that there is no friction, only gravity. Speed will always be the same when two objects are dropped from the same height at the same time. Thus, the ratio 1:1 is correct with reference to the rock and the stone. return to top
Answer 2
2:1 INCORRECT Theoretically, all objects should fall with an equal speed regardless of the object's weight or shape. However, in the Earth's atmosphere, air friction prevents this law from being completely true. Thus, a feather will fall to earth more slowly than would a pencil, due to the increased available surface area of a feather. Despite this, when we are given a question such as this, "Free Fall"-- speed will always be the same when two objects are dropped from the same height at the same time. Thus, answer 2 cannot be correct; if it were, the rock would be going twice as fast as the stone, and because of the above law this cannot be true. return to top
Answer 3
1:2 INCORRECT Theoretically, all objects should fall with an equal speed regardless of the object's weight or shape. However, in the Earth's atmosphere, air friction prevents this law from being completely true. Thus, a feather will fall to earth more slowly than would a pencil, due to the increased available surface area of a feather. Despite this, when we are given a question such as this, "Free Fall"-- speed will always be the same when two objects are dropped from the same height at the same time. Thus, answer 3 cannot be correct; if it were, the stone would have to be going faster than the rock, but, because of the above reasons, they both must be going the same speed, and answer 3 is incorrect. return to top
Answer 4
4:1 INCORRECT Theoretically, all objects should fall with an equal speed regardless of the object's weight or shape. However, in the Earth's atmosphere, air friction prevents this law from being completely true. Thus, a feather will fall to earth more slowly than would a pencil, due to the increased available surface area of a feather. Despite this, when we are given a question such as this, "Free Fall"-- speed will always be the same when two objects are dropped from the same height at the same time. Thus, answer 4 cannot be correct; if it were, the rock would have to be going four times the speed of the stone, but, because of the above information, we know that this is not possible. Answer 4 is incorrect. return to top
What's this question really asking?
Do you know the basic rules of gravity and freefall? return to top |

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