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- A speeding car changes its velocity from 108 kmh-' to 36 kmh in 4 s. Calculate
deceleration in (i) ms 2 (ii) kmh 2.
[(i) 5 ms (ii) 64800 kmh]answers
Answers
ANSWER:
Retardation = 5 m/s²
Retardation = 64800 km/h²
___________________
Explanation:
given that,
A speeding car changes its velocity from 108 kmh-' to 36 kmh in 4 s.
so,
here,
initial velocity of car = 108 km/s
changing it into m/s
=> 108 × 1000 m/60 × 60s
= 6 × 5
30 m/s
final velocity of car are = 36 km/h
changing it into m/s
36 × 1000 m/60 × 60 s
= 10 m/s
tine taken for decelerating = 4 seconds
➡deceleration in
(i) ms
now,
we have,
initial velocity(u) = 30 m/s
final velocity(v) = 10 m/s
tine taken(t) = 4 seconds
by the equation of motion
v = u + at
where a shows the acceleration
putting the values,
10 = 30 + a(4)
4a + 30 = 10
4a = 10 - 30
4a = -20
a = -20/4
a = -5 m/s²
negation of acceleration shows the retardation
so,
Retardation = 5 m/s²
(ii) km/h
in km/h
we have retardation = 5 m/s²
1 m = 1/1000 km
5 m = 1/1000 × 5 km
= 5 m = 1/200 km
1 s = 1/60 h
s² = 1/(60 × 60 × 60 × 60)h
s² = 1/12960000 h
now,
5 m/s²
= (1/200 km)/(1/12960000 )h
= 12960000/200
= 64800 km/h²
so,