Answer:
[tex]\huge\boxed{\sf V_i=60 \ m/s}[/tex]
Explanation:
Given Data:
Final speed = [tex]V_f[/tex] = 40 m/s
Time = t = 5 s
Acceleration = a = -4 m/s²
Required:
Initial velocity = [tex]V_i[/tex] = ?
Formula:
[tex]\displaystyle a = \frac{V_f-V_i}{t}[/tex]
Solution:
Put the givens in the above formula
[tex]\displaystyle -4=\frac{40 - V_i}{5} \\\\Multiply \ -5 \ to \ both \ sides\\\\-4 \times 5 = 40 - V_i\\\\-20 =40-V_i\\\\Subtract \ 40 \ to \ both \ sides\\\\-20-40=-V_i\\\\-60\ m/s=-V_i\\\\60 \ m/s = V_i\\\\V_i=60 \ m/s\\\\\rule[225]{225}{2}[/tex]
