Question

4. An automobile travelling with an inital
Velocity O Bom/sec. comes to nest after
travelling a distance of gom. Assuming the
retardation to be uniform find its value
What time does it takes to cover the distances​

Answer 1

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11th

Physics

Motion in a Straight Line

Stopping Distance and Reaction Time

An automobile travelling wi...

PHYSICS

An automobile travelling with a speed of 60km/h, can apply brake to stop within a distance of 20m. If the car is going twice as fast i.e., 120km/h, the stopping distance will be

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ANSWER

Here we use 3

rd

equation of motion,

v

2

=u

2

+2as, where v= final velocity u= initial velocity,

a= acceleration due to gravity, s= Distance or height.

For first case u

1

=0m/s, v

1

=60km/h=

18

5

×60m/s=

3

50

m/s,a

1

=a,s

1

=d

1

=20m

0=v

1

2

−2×a×d

1

⇒v

1

2

=2ad

1

.............(1)

For second case u

2

=0m/s, v

1

=120km/h=

18

5

×120 m/s=

3

100

m/s,a

2

=a,s

2

=d

2

0=v

2

2

−2ad

2

⇒v

2

2

=2×a×d

2

⇒4v

1

2

=2ad

2

..............(2)

When equation (2) is divided by equation (1) we get,

v

1

2

4v

1

2

=

2×a×d

1

2×a×d

2

⇒

d

1

d

2

=4

d

2

=4×d

1

⇒d

2

=4×20⇒d

2

=80m