A) Time needed: 6.24 s
B) Time needed: 2.86 s
Explanation:
A)
In this part, we are told that the power if the engine is constant. The power of the engine is given by
![P=\frac{W}{t}](https://tex.z-dn.net/?f=P%3D%5Cfrac%7BW%7D%7Bt%7D)
where
W is the work done
t is the time
This means that the power of the engine is proportional to the work done, and therefore, to the kinetic energy of the car:
![P=\frac{\frac{1}{2}mv^2}{t}=const.](https://tex.z-dn.net/?f=P%3D%5Cfrac%7B%5Cfrac%7B1%7D%7B2%7Dmv%5E2%7D%7Bt%7D%3Dconst.)
where m is the mass of the car and v its velocity.
SInce power is constant, we can write:
![\frac{\frac{1}{2}mv_1^2}{t_1^2}=\frac{\frac{1}{2}mv_2^2}{t_2}](https://tex.z-dn.net/?f=%5Cfrac%7B%5Cfrac%7B1%7D%7B2%7Dmv_1%5E2%7D%7Bt_1%5E2%7D%3D%5Cfrac%7B%5Cfrac%7B1%7D%7B2%7Dmv_2%5E2%7D%7Bt_2%7D)
where:
is the time the car needs to accelerates to ![v_1=28.0 mph](https://tex.z-dn.net/?f=v_1%3D28.0%20mph)
is the time the car needs to accelerate to ![v_2=57.0 mph](https://tex.z-dn.net/?f=v_2%3D57.0%20mph)
Therefore, solving for
,
![t_2 = \frac{v^2}{u^2}t_1=\frac{57^2}{28^2}(1.40)=6.24 s](https://tex.z-dn.net/?f=t_2%20%3D%20%5Cfrac%7Bv%5E2%7D%7Bu%5E2%7Dt_1%3D%5Cfrac%7B57%5E2%7D%7B28%5E2%7D%281.40%29%3D6.24%20s)
B)
First of all, we have to calculate the acceleration of the car. We can do it using the following equation:
![a=\frac{v-u}{t}](https://tex.z-dn.net/?f=a%3D%5Cfrac%7Bv-u%7D%7Bt%7D)
where:
u = 0 is the initial velocity
is the final velocity
t = 1.40 s is the time elapsed
Substituting, we find the acceleration:
![a=\frac{12.5-0}{1.40}=8.9 m/s^2](https://tex.z-dn.net/?f=a%3D%5Cfrac%7B12.5-0%7D%7B1.40%7D%3D8.9%20m%2Fs%5E2)
In this part, we are told that the force exerted by the engine is constant: according to Newton's second law, acceleration is proportional to the force,
![F=ma](https://tex.z-dn.net/?f=F%3Dma)
This means that the acceleration is also constant.
Now we want to find how long the car takes to accelerate to a final velocity of
![v=57.0 mph \cdot \frac{1609}{3600}=25.5 m/s](https://tex.z-dn.net/?f=v%3D57.0%20mph%20%5Ccdot%20%5Cfrac%7B1609%7D%7B3600%7D%3D25.5%20m%2Fs)
From an initial velocity of
u = 0
Using again the same suvat equation, and using the acceleration we found previously, we find:
![t=\frac{v-u}{a}=\frac{25.5-0}{8.9}=2.87 s](https://tex.z-dn.net/?f=t%3D%5Cfrac%7Bv-u%7D%7Ba%7D%3D%5Cfrac%7B25.5-0%7D%7B8.9%7D%3D2.87%20s)
Learn more about accelerated motion:
brainly.com/question/9527152
brainly.com/question/11181826
brainly.com/question/2506873
brainly.com/question/2562700
About power:
brainly.com/question/7956557
#LearnwithBrainly