Question

1) What would the average acceleration be for a car at a stoplight that speeds up to 20 m/s in 10 seconds (in m/s^2)

2) Imagine that a car traveling at 100 m/s must slam on the brakes to avoid hitting a raccoon. If it takes 4 seconds for the car to slow down to a stop, what is its acceleration (in m/s^2)

Answer 1

1.)
Velocity is in m/s, and acceleration is in m/s^2 like you said. Because of this, we can calculate this by dividing the speed by the time it took to get to that speed.
(20 meters/second) / 10 seconds = 2 meters/ second^2

2.)
Same thing with the first one.
(100 meters/second) / 4 seconds = 25 meters / seconds^2

Answer 2

Answer:

Part a)

a = 2 m/s/s

Part b)

a = - 25 m/s/s

Explanation:

As we know that the average acceleration id defined as the rate of change in the velocity of the object

so here it is given by formula

$a = \frac{v_f - v_i}{\Delta t}$

now we know that

$v_f = 20 m/s$

$v_i = 0$

$\Delta t = 10 s$

now we have

$a = \frac{20 - 0}{10} = 2 m/s^2$

Part b)

here car is travelling with speed 100 m/s

now driver slams brakes and car finally stop in t = 4 s

so the average acceleration is given as

$a = \frac{v_f - v_i}{\Delta t}$

now we know that

$v_f = 0 m/s$

$v_i = 100$

$\Delta t = 4 s$

now we have

$a = \frac{0 - 100}{4} = -25 m/s^2$