Can someone please help me solve all of these four problems as soon as possible

Question

Can someone please help me solve all of these four problems as soon as possible please? Can you please show me step by step because I was keep getting the wrong answers for these four.

An electric vehicle starts from rest and accelerates at a rate of 2.2 m/s2 in a straight line until it reaches a speed of 21 m/s. The vehicle then slows at a constant rate of 1.4 m/s2 until it stops. (a) How much time elapses from start to stop? (b) How far does the vehicle move from start to stop? (a) Number Units (b) Number Units

Explanation / Answer

1)

Vf = at + Vi

Vf = final velocity (21m/s)
a = acceleration (2.2m/s^2)
t = time
Vi = initial velocity (0m/s)

21 = 2.2t + 0
t = 9.54s

Find the distance as the car accelerates
Xf = .5at^2 + Vt + Xi

Xf = final position
Xi = initial position
Xf = .5(2.2)(9.54)^2
Xf = 100.1m


Vf = at + Vi

now that the car decelerates, its inital veloicty at the time is 21m/s. When the car stops, its final velocity is 0m/s
0 = -1t + 21
-21 = -t
t = 21s

find the distance as it decelerates
Xf = .5at^2 + Vt + Xi
Xf = .5(-1)(21)^2 + 21(21)
Xf = 220.5m

the total time is 9.54 + 21 = 30.54s
the total distance is 220.5 + 100.1= 320.6m

2)

55.5 km/h = 15.41 m/s

s = Vo t + ½ a t²

23.6 = (15.41)(1.86) + ½ a (1.86)²

a = -1.73 m/s²

V = v + a t

V = 15.41 + (-1.73)(1.86)

V = 12.2 m/s

3)

Apple 1:

s = ut + (1/2) at2

y = 0 + (1/2) ( 9.8 ) 22 ................ ( initial velocity zero because apple is just dropped )

= 19.6 m

4)

Apple 2

s = 20 m; a = 10 m/s2 ; t = 1.25s

s = ut + 1/2 at2

20 = u * 1.25 + 1/2 * 10 * 1.252

1.25u = 20 - 7.8125

u = 12.1875 / 1.25

u = 9.75m/s (final answer)

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