Question

question 8 (1 point)
suppose that a car traveling to the west (-x direction) begins to slow down as it approaches a traffic light. make a statement concerning its acceleration.
the car is decelerating, and its acceleration is positive.
the car is decelerating, and its acceleration is negative.
the acceleration is zero.
a statement cannot be made using the information given.
question 9 (1 point)
an airplane increases its speed from 100 m/s to 160 m/s, at the average rate of 15 m/s2. how much time does it take for the complete increase in speed?
17 s
0.058 s
4.0 s
0.25 s
question 10 (1 point)
if the position versus time graph of an object is a horizontal line, the object is
moving with constant non - zero speed.
moving with constant non - zero acceleration.
at rest.
moving with infinite speed.

Explanation:

Question 8

The car is moving in the -x (West) direction and slowing down. Deceleration means the acceleration is opposite to the velocity direction. Since velocity is negative (West), acceleration opposite (positive) causes slowing. So decelerating with positive acceleration.

Step1: Recall the acceleration formula

Acceleration \( a = \frac{\Delta v}{\Delta t} \), so \( \Delta t = \frac{\Delta v}{a} \).

Step2: Calculate change in velocity

\( \Delta v = 160 - 100 = 60 \, \text{m/s} \).

Step3: Solve for time

\( \Delta t = \frac{60}{15} = 4.0 \, \text{s} \).

A position - time graph with a horizontal line means position doesn't change over time. Speed is the rate of change of position (\( v=\frac{\Delta x}{\Delta t} \)). If \( \Delta x = 0 \), speed is 0, so the object is at rest.

Answer:

A. The car is decelerating, and its acceleration is positive.

Question 9