Q13. A stone is dropped from a height of 5 km. The distance it falls through varies directly with the
2 answers:
Answer:
<em>The stone covers 36 m in the 5th second. Correct choice: A.</em>
Step-by-step explanation:
<u>Proportions</u>
Two variables are said to be proportional if one of them can be calculated by multiplying the other by a constant of proportionality. If y and x are those variables, then:
y=k.x
There are other similar proportions where the relation is not linear. For example, if y is proportional to the square of x, then:
According to the conditions of the question, the distance traveled by a stone dropped from a height of 5 Km varies directly with the square of the time taken to fall through that distance. If d is the distance and t is the time, then;
To find the value of k, we use the given condition: The stone falls d=66 meters in t=4 seconds. Substituting:
Solving:
Substitute the value of k into the equation to get the complete model.
Now we calculate the distance when t=5 seconds:
The stone has covered 100 m in 5 seconds. But we need to find the distance covered in the 5th second, that specific interval between 4 sec and 5 sec.
Since we already know the distance for t=4 sec (64 m), and the distance for t=5 sec (100 m), then:
distance in the 5th second = 100 m - 64 m = 36 m
The stone covers 36 m in the 5th second. Option A.
You might be interested in
The system of inequalities is the following:
i) <span>y ≤ –0.75x
ii)</span><span>y ≤ 3x – 2
since </span>
, we can write the system again as
Whenever we are asked to sketch the solution of a system of linear inequalities, we:
1. Draw the lines
2. Color the regions of the inequalities.
3. The solution is the region colored twice.
A.
to draw the line
consider the points: (-4, 1) and (0, 0), or any 2 other points (x,y) for which hold.
since we have an "smaller or equal to" inequality, the line is a solid line (not dashed, or dotted).
In order to find out which region of the line to color, consider a point not on the line, for example P(1, 1), which is clearly in the upper region of the line.
For (x, y)=(1, 1) the inequality
, does not hold because
is not true,
this means that the solution is the region of the line not containing (1, 1), as shown in picture 1.
B.
similarly, to draw the solution of inequality ii) y ≤ 3x – 2,
we first draw the line y=3x-2, using the points (0, -2) and (2, 4), or any other 2 points (x,y) for which y=3x-2 holds.
after we draw the line, we can check the point P(1, 7) which clearly is above the line y=3x-2.
for (x, y) = (1, 7), the inequality y ≤ 3x – 2 does not hold
because 7 is not ≤ 3*1-2=1, so the region we color is the one not containing P(1, 7), as shown in picture 2.
The solution of the system is the region colored with both colors, the solid lines included. Check picture 3.
the lines intersect at (0.533, -0.4) because:
–0.75x=3x-2
-0.75x-3x=-2
-3.75x=-2, that is x= -2/(-3.75)=0.533
for x=0.533, y=3x-2=3(0.533)-2=-0.4
Answer: Picture 3, the half-lines included. So the graph is in the 3rd and 4th Quadrants
i) <span>y ≤ –0.75x
ii)</span><span>y ≤ 3x – 2
since </span>
Whenever we are asked to sketch the solution of a system of linear inequalities, we:
1. Draw the lines
2. Color the regions of the inequalities.
3. The solution is the region colored twice.
A.
to draw the line
consider the points: (-4, 1) and (0, 0), or any 2 other points (x,y) for which
since we have an "smaller or equal to" inequality, the line is a solid line (not dashed, or dotted).
In order to find out which region of the line to color, consider a point not on the line, for example P(1, 1), which is clearly in the upper region of the line.
For (x, y)=(1, 1) the inequality
this means that the solution is the region of the line not containing (1, 1), as shown in picture 1.
B.
similarly, to draw the solution of inequality ii) y ≤ 3x – 2,
we first draw the line y=3x-2, using the points (0, -2) and (2, 4), or any other 2 points (x,y) for which y=3x-2 holds.
after we draw the line, we can check the point P(1, 7) which clearly is above the line y=3x-2.
for (x, y) = (1, 7), the inequality y ≤ 3x – 2 does not hold
because 7 is not ≤ 3*1-2=1, so the region we color is the one not containing P(1, 7), as shown in picture 2.
The solution of the system is the region colored with both colors, the solid lines included. Check picture 3.
the lines intersect at (0.533, -0.4) because:
–0.75x=3x-2
-0.75x-3x=-2
-3.75x=-2, that is x= -2/(-3.75)=0.533
for x=0.533, y=3x-2=3(0.533)-2=-0.4
Answer: Picture 3, the half-lines included. So the graph is in the 3rd and 4th Quadrants