RIO SALADO - PHY 111 MIDTERM 1 2025 UPDATED ACTUAL EXAM
WITH CORRECT SOLUTIONS.
Question 1
A student moves 8.0 m to the west, 6.0 m to the north, and 10.0 m to the east. What is the
magnitude of the displacement?
A) 6.0 m
B) 8.0 m
C) 10.0 m
D) 6.3 m
E) 24.0 m
Correct Answer: D) 6.3 m
Rationale: First, find the net displacement in the East-West direction: 10.0 m (East) - 8.0 m
(West) = 2.0 m (East).
The displacement in the North-South direction is 6.0 m (North).
To find the magnitude of the total displacement, use the Pythagorean theorem for the
perpendicular components:
Magnitude = sqrt((2.0 m)^2 + (6.0 m)^2) = sqrt(4.0 + 36.0) = sqrt(40.0) ≈ 6.32 m. Rounded
to two significant figures, this is 6.3 m.
Question 2
Examine the position vs. time graph where position decreases linearly with time. What is the
velocity of the object at t = 5.0 s?
A) 0 m/s
B) 5 m/s
C) -5 m/s
D) 10 m/s
E) -10 m/s
Correct Answer: C) -5 m/s
Rationale: On a position vs. time graph, the velocity is represented by the slope of the line. If
the position is decreasing linearly, the slope is negative and constant. Assuming the graph
shows a change in position (Δx) of -10 m over a time interval (Δt) of 2 s (e.g., from x=10m at
t=0s to x=0m at t=2s, then further down), the slope would be -10m/2s = -5 m/s. Since the
velocity is constant, it is -5 m/s at any point, including t = 5.0 s.
Question 3
A student measures the mass of an object at 4.68 g and the volume of the object at 2.3 mL. The
student calculates the density as 2.03478 g/mL. A second student disagrees with the density
calculation. Which of the following statements would explain why the second student disagrees?
A) The mass measurement is incorrect.
B) The volume measurement is incorrect.
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C) The density calculation is mathematically incorrect.
D) The number of decimals in the answer does not show proper precision.
E) The units for density are incorrect.
Correct Answer: D) The number of decimals in the answer does not show proper precision.
Rationale: When multiplying or dividing measurements, the result should have the same
number of significant figures as the measurement with the fewest significant figures. Here,
mass (4.68 g) has three significant figures, but volume (2.3 mL) has only two. Therefore, the
density should be reported with two significant figures (2.0 g/mL), not five decimal places
(2.03478 g/mL). The second student is correct about the precision.
Question 4
Examine the position vs. time graph. If the graph shows an initial straight line with a positive
slope, followed by another straight line with a negative slope, which of the following correctly
describes the motion of the object?
A) Moving forwards and then standing still.
B) Moving backwards and then moving forwards.
C) Accelerating forwards and then slowing down.
D) Forwards at a constant speed and then backward at a constant speed.
E) Standing still and then moving backwards.
Correct Answer: D) Forwards at a constant speed and then backward at a constant speed
Rationale: On a position vs. time graph, a straight line indicates constant velocity (constant
speed). A positive slope means moving in the positive direction (forwards), and a negative
slope means moving in the negative direction (backwards).
Question 5
A car moving at a constant 25 m/s travels for 3.0 seconds. What is the distance traveled by the
car?
A) 8.3 m
B) 25 m
C) 75 m
D) 100 m
E) 150 m
Correct Answer: C) 75 m
Rationale: For constant speed motion, distance = speed × time.
Distance = 25 m/s × 3.0 s = 75 m.
Question 6
A student measures the mass of an object at 4.68 g. Which of the following statements is most
accurate regarding significant figures?
A) All three digits are estimated.
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B) The first digit is measured, and the last two digits are estimated.
C) The first two digits are measured and the last digit is estimated.
D) All three digits are measured precisely.
E) The last digit is always exact.
Correct Answer: C) he first two digits are measured and the last digit is estimated.
Rationale: In scientific measurement, all digits that are known with certainty plus one
estimated (uncertain) digit are considered significant figures. So, in 4.68 g, the '4' and '6'
are measured with certainty, and the '8' is the estimated digit.
Question 7
A student models the constant speed motion of an object with the following equation: x = (4 m/s)
t + (-15 m). Which of the following descriptions of motion is consistent with this equation?
A) The object starts at a positive position and travels backwards.
B) The object starts at a negative position and travels backwards.
C) The object starts at a positive position and travels forwards.
D) The object starts at a negative position and travels forwards.
E) The object remains at a constant position.
Correct Answer: D) The object starts at a negative position and travels forwards.
Rationale: The equation of motion for constant velocity is x = v*t + x_initial.
Comparing this to x = (4 m/s) t + (-15 m):
The initial position (x_initial) is -15 m, which means the object starts at a negative position.
The velocity (v) is 4 m/s. Since it's positive, the object is traveling forwards.
Question 8
How much time will it take for an object traveling at a constant speed of 20 m/s to travel 15 m?
A) 1.33 s
B) 0.75 s
C) 20 s
D) 15 s
E) 300 s
Correct Answer: B) 0.75 s
Rationale: For constant speed motion, time = distance / speed.
Time = 15 m / 20 m/s = 0.75 s.
Question 9
A student models the constant speed motion of an object with the following equation: x = (-2
m/s) t + (4 m). Which of the following descriptions of motion is consistent with this equation?
A) The object starts at a negative position and travels forwards.
B) The object starts at a positive position and travels forwards.
C) The object starts at a negative position and travels backwards.
WITH CORRECT SOLUTIONS.
Question 1
A student moves 8.0 m to the west, 6.0 m to the north, and 10.0 m to the east. What is the
magnitude of the displacement?
A) 6.0 m
B) 8.0 m
C) 10.0 m
D) 6.3 m
E) 24.0 m
Correct Answer: D) 6.3 m
Rationale: First, find the net displacement in the East-West direction: 10.0 m (East) - 8.0 m
(West) = 2.0 m (East).
The displacement in the North-South direction is 6.0 m (North).
To find the magnitude of the total displacement, use the Pythagorean theorem for the
perpendicular components:
Magnitude = sqrt((2.0 m)^2 + (6.0 m)^2) = sqrt(4.0 + 36.0) = sqrt(40.0) ≈ 6.32 m. Rounded
to two significant figures, this is 6.3 m.
Question 2
Examine the position vs. time graph where position decreases linearly with time. What is the
velocity of the object at t = 5.0 s?
A) 0 m/s
B) 5 m/s
C) -5 m/s
D) 10 m/s
E) -10 m/s
Correct Answer: C) -5 m/s
Rationale: On a position vs. time graph, the velocity is represented by the slope of the line. If
the position is decreasing linearly, the slope is negative and constant. Assuming the graph
shows a change in position (Δx) of -10 m over a time interval (Δt) of 2 s (e.g., from x=10m at
t=0s to x=0m at t=2s, then further down), the slope would be -10m/2s = -5 m/s. Since the
velocity is constant, it is -5 m/s at any point, including t = 5.0 s.
Question 3
A student measures the mass of an object at 4.68 g and the volume of the object at 2.3 mL. The
student calculates the density as 2.03478 g/mL. A second student disagrees with the density
calculation. Which of the following statements would explain why the second student disagrees?
A) The mass measurement is incorrect.
B) The volume measurement is incorrect.
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C) The density calculation is mathematically incorrect.
D) The number of decimals in the answer does not show proper precision.
E) The units for density are incorrect.
Correct Answer: D) The number of decimals in the answer does not show proper precision.
Rationale: When multiplying or dividing measurements, the result should have the same
number of significant figures as the measurement with the fewest significant figures. Here,
mass (4.68 g) has three significant figures, but volume (2.3 mL) has only two. Therefore, the
density should be reported with two significant figures (2.0 g/mL), not five decimal places
(2.03478 g/mL). The second student is correct about the precision.
Question 4
Examine the position vs. time graph. If the graph shows an initial straight line with a positive
slope, followed by another straight line with a negative slope, which of the following correctly
describes the motion of the object?
A) Moving forwards and then standing still.
B) Moving backwards and then moving forwards.
C) Accelerating forwards and then slowing down.
D) Forwards at a constant speed and then backward at a constant speed.
E) Standing still and then moving backwards.
Correct Answer: D) Forwards at a constant speed and then backward at a constant speed
Rationale: On a position vs. time graph, a straight line indicates constant velocity (constant
speed). A positive slope means moving in the positive direction (forwards), and a negative
slope means moving in the negative direction (backwards).
Question 5
A car moving at a constant 25 m/s travels for 3.0 seconds. What is the distance traveled by the
car?
A) 8.3 m
B) 25 m
C) 75 m
D) 100 m
E) 150 m
Correct Answer: C) 75 m
Rationale: For constant speed motion, distance = speed × time.
Distance = 25 m/s × 3.0 s = 75 m.
Question 6
A student measures the mass of an object at 4.68 g. Which of the following statements is most
accurate regarding significant figures?
A) All three digits are estimated.
, [Type here]
B) The first digit is measured, and the last two digits are estimated.
C) The first two digits are measured and the last digit is estimated.
D) All three digits are measured precisely.
E) The last digit is always exact.
Correct Answer: C) he first two digits are measured and the last digit is estimated.
Rationale: In scientific measurement, all digits that are known with certainty plus one
estimated (uncertain) digit are considered significant figures. So, in 4.68 g, the '4' and '6'
are measured with certainty, and the '8' is the estimated digit.
Question 7
A student models the constant speed motion of an object with the following equation: x = (4 m/s)
t + (-15 m). Which of the following descriptions of motion is consistent with this equation?
A) The object starts at a positive position and travels backwards.
B) The object starts at a negative position and travels backwards.
C) The object starts at a positive position and travels forwards.
D) The object starts at a negative position and travels forwards.
E) The object remains at a constant position.
Correct Answer: D) The object starts at a negative position and travels forwards.
Rationale: The equation of motion for constant velocity is x = v*t + x_initial.
Comparing this to x = (4 m/s) t + (-15 m):
The initial position (x_initial) is -15 m, which means the object starts at a negative position.
The velocity (v) is 4 m/s. Since it's positive, the object is traveling forwards.
Question 8
How much time will it take for an object traveling at a constant speed of 20 m/s to travel 15 m?
A) 1.33 s
B) 0.75 s
C) 20 s
D) 15 s
E) 300 s
Correct Answer: B) 0.75 s
Rationale: For constant speed motion, time = distance / speed.
Time = 15 m / 20 m/s = 0.75 s.
Question 9
A student models the constant speed motion of an object with the following equation: x = (-2
m/s) t + (4 m). Which of the following descriptions of motion is consistent with this equation?
A) The object starts at a negative position and travels forwards.
B) The object starts at a positive position and travels forwards.
C) The object starts at a negative position and travels backwards.
