Question

A body moving with20 m/s slow down to 10 m/s. find acceleration and time taken in covering 20 m.(for solve class 9th )
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Answer 1

QUESTION:

A body moving with20 m/s slow down to 10 m/s. find acceleration and time taken in covering 20 m.

ANSWER:

Acceleration = -7.5 m/s²

time to cover 20 meter = 1.3 seconds

Explanation:

given that,

A body moving with 20 m/s slow down to 10 m/s

here,

we have,

initial velocity of the body = 20 m/s

and,

final velocity of the body = 10 m/s

also,

given that the distance covered by the body after decelerating = 20 m

let the time taken to cover 20 m after decelerating be t

now,

we have,

initial velocity(u) = 20 m/s

final velocity(v) = 10 m/s

distance travelled(s) = 20 m

by the equation of motion

v² = u² + 2as

putting the values,

(10)² = (20)² + 2a(20)

100 = 400 + 40a

40a + 400 = 100

40a = 100 - 400

40a = -300

a = -300/40

a = -7.5 m/s²

So

Acceleration = -7.5 m/s²

now,

we have,

initial velocity(u) = 20 m/s

final velocity(v) = 10 m/s

Acceleration(a) = -7.5 m/s²

distance covered(s) = 20 m

let the time taken to decelerating be t

by the equation of motion

v = u + at

putting the values,

10 = 20 + (-7.5)t

-7.5t + 20 = 10

-7.5t = 10 - 20

-7.5t = -10

t = -10/-7.5

t = 1.3 s

so

time to cover 20 meter = 1.3 seconds

Answer 2

Explanation:

u = 20 m/s

v= 10 m/s

s= 20 m

v² = u² + 2as

(10)² = (20)² + 2a(20)

100 = 400 + 40a

40a + 400 = 100

40a = 100 - 400

40a = -300

a = -300/40

a = -7.5 m/s²

So

Acceleration = -7.5 m/s²

so

time to cover 20 meter = 1.3 seconds