Question

24. A car moves with speed 72 km/hr. What is its speed in
m/s ? What is acceleration or retardation produced in
the car if it stops on applying the brakes in 4 seconds?​

Answer 1

Answer:

Speed = 72 × 5 / 18

= 4 × 5

= 20 m/sec.

v = u + at

0 = 72 + 4a

-72 = 4a

a = -18 m/sec.^2

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Answer 2

Explanation:

Given speed of the vehicle=72㎞/hr

=72×

18

5

=20m/s

radius of the wheel =

2

0.5

=0.25

initial angular velocity (ω

0

)=

0.25

20

=80rad/s

angle covered after applying brakes=20×2π=40π

let the angular retardation be −αrad/s

2

final angular momentum ω=0

putting formula ω

2

=ω

0

2

−2αθ

⇒0=ω

0

2

−2×α×θ

⇒ω

0

2

=2×α×θ

⇒80

2

=2×α×40×π

⇒α=

80×π

80

2

⇒α=

π

80

putting the value of π=3.14

α=25.47rad/s

2

so retardation is −25.477≅−25.5 rad/s

2