In a test run, a certain car accelerates uniformly from zero to 24.0 m/s in 2.95 s. (a) What is the magnitude of the car’s acceleration? (b) How long does it take the car to change its speed from 10.0 m/s to 20.0 m/s? (c) Will doubling the time always double the change in speed? Why?

Respuesta :

a. The thing that needs to be found is the magnitude of the car’s acceleration. We already know that 
Acceleration = Velocity/Time
                     = 24/2.95 m/s^2
                     = 8.136 m/s^2

b. Initial velocity = 10 m/s
Final velocity = 20 m/s
Let us assume the time taken = t
Then
(20 - 10)/t = 8.136
8.136t = 10
t = 10/8.136
  = 1.229 seconds

c. No, doubling the time will half the speed if all other conditions remain the same.

(a) 8.14 m/s^2

Explanation:

Acceleration of the car is given by:

[tex]a=\frac{v-u}{t}[/tex]

where

u = 0 is the initial velocity

v = 24.0 m/s is the final velocity

t = 2.95 s is the time taken

Substituting numbers into the equation, we find

[tex]a=\frac{24.0 m/s-0}{2.95 s}=8.14 m/s^2[/tex]


(b) 1.23 s

Explanation:

We can use the same formula for the acceleration:

[tex]a=\frac{v-u}{t}[/tex]

where this time, we have

u = 10.0 m/s

v = 20.0 m/s

a = 8.14 m/s^2

Substituting numbers into the equation, we can find the time taken, t:

[tex]t=\frac{v-u}{a}=\frac{20.0 m/s-10.0 m/s}{8.14 m/s^2}=1.23 s[/tex]


c) If the acceleration is constant, yes

Explanation:

Let's take again the equation for the acceleration:

[tex]a=\frac{v-u}{t}[/tex]

We can rewrite it as:

[tex](v-u) = at[/tex]

where the term (v-u) represents the change in velocity. From the formula we see that, if a (acceleration) is constant, then (v-u) is directly proportional to the time t: therefore, if t doubles, the change in velocity (v-u) doubles as well.