Question

how long will it take steve to run 85 m if he can run 3.4 m/s?
problem 3:
calculate the average speeds of object a and object b. which object has the faster speed?
how can you answer this question without doing math?
problem 4:
what is the average speed of the object between b and c?

Explanation:

Step1: Recall speed - time - distance formula

The formula for speed is $v=\frac{d}{t}$, where $v$ is speed, $d$ is distance, and $t$ is time. We want to find $t$, so we can re - arrange the formula to $t = \frac{d}{v}$.

Step2: Substitute given values

We are given that $d = 85$ m and $v=3.4$ m/s. Substituting these values into the formula $t=\frac{d}{v}$, we get $t=\frac{85}{3.4}$.

Step3: Calculate the time

$\frac{85}{3.4}=25$ s.

for Problem 3:

Step1: Recall average - speed formula

The average - speed formula is $v_{avg}=\frac{\Delta d}{\Delta t}$, where $\Delta d$ is the change in distance and $\Delta t$ is the change in time.
For object A: From the graph, $\Delta d_A = 15$ km and $\Delta t_A=11 - 9=2$ hours. So, $v_{avgA}=\frac{15}{2}=7.5$ km/h.
For object B: From the graph, $\Delta d_B = 15$ km and $\Delta t_B = 11 - 9 = 2$ hours. So, $v_{avgB}=\frac{15}{2}=7.5$ km/h.
To answer without doing math, we can observe that the lines representing the motion of A and B are parallel, which means they have the same slope. In a distance - time graph, the slope of the line represents the speed. So, they have the same speed.

for Problem 4:

Step1: Determine $\Delta d$ and $\Delta t$

From the graph, at point B, let's assume the distance $d_B = 6$ km and at point C, $d_C = 6$ km. So, $\Delta d=d_C - d_B=6 - 6 = 0$ km.
Let's assume the time at B is $t_B = 20$ units and at C is $t_C = 35$ units. So, $\Delta t=t_C - t_B=35 - 20 = 15$ units.

Step2: Calculate average speed

Using the formula $v_{avg}=\frac{\Delta d}{\Delta t}$, we substitute $\Delta d = 0$ km and $\Delta t = 15$ units. So, $v_{avg}=\frac{0}{15}=0$ km/h.

Answer:

25 s