In: Physics
An electric vehicle starts from rest and accelerates at a rate of 2.1 m/s2 in a straight line until it reaches a speed of 17 m/s. The vehicle then slows at a constant rate of 1.1 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? solve both a b show units
Given : a= 2.1 m/s2 , a' = -1.1 m/s2 , v= 17 m/s
Solution :
(a) Total time elapses from start to stop
Using equation of motion to find time required to reach velocity 17 m/s :
v = v0+at1
17 m/s = 0 +(2.1m/s2)t1
t1 = 17/2.1 = 8.1 s
Using equation of motion to find time requured to stop from 17 m/s velocity :
v = v0 +a't2
0 = (17m/s)+ (-1.1 m/s2)t2
t2 = 17/1.1 = 15.4 s
Total time elapses from start to stop is given by: t = t1 + t2
i.e. t = 8.1 s + 15.4 s = 23.5 s
Answer : 23.5 s
(b) Total distance travelled by vehicle from start to stop
Using equation of motion to find the distance traveled to reach velocity 17 m/s :
v2 = v02+2ad1
d1 = (v2-v02)/2a
= [(17)2-0]/2(2.1)
= 68.8 m
Using equation of motion to find the distance traveled to stop from velcoti 17 m/s
v2 = v02+2a'd2
d2 = (v2-v02)/2a'
= [(0)-(17)2]/2(-1.1)
= 131.4 m
Total distance traveled from start to stop is given by:
d = d1 + d2
= 68.8 m + 131.4 m
= 200.2 m
Answer : 200.2 m