Question

an object starting from rest travels 20 metres in the first 2 seconds,and 100 metres in the next 10 seconds . what will be the velocity after 7 seconds from start.​

Answer 1

ANSWER:

• The velocity of the object after 7 seconds from start = 6 m/s.

GIVEN:

• An object starting from rest travels 20 metres in the first 2 seconds.

• It travels 100 metres in the next 10 seconds.

TO FIND:

• The velocity of the object after 7 seconds from start.

EXPLANATION:

★ S = ut + 1/2 at²

•°• S = 20m

•°• u = 0

•°• t = 2 s

•°• 20 = 0 + 1/2 a(2)²

•°• 2a = 20

•°• a = 10 m/s²

★ v² - u² = 2 aS

°•° u = 0

°•° a = 10 m/s²

°•° S = 20 m

°•° v² - 0² = 2(10)(20)

°•° v² = 400

°•° v = 20 m/s

★ S = ut + 1/2 at²

•°• S = 100

•°• u = 20 m/s (Velocity after 2 s.)

•°• t = 10 s

•°• 100 = 20(10) + 1/2 a(10)²

•°• 1/2 a × 100 = - 100

•°• a = - 2 m/s²

★ v = u + at

°•° v = velocity at 7 seconds.

°•° u = 20 m/s (Velocity after 2 s.)

°•° a = - 2 m/s² (Acceleration after 2 s.)

°•° t = 7 s

°•° v = 20 + ( - 2)(7)

°•° v = 20 - 14

°•° v = 6 m/s

Hence the velocity of the object after 7 seconds from start = 6 m/s.

Answer 2

Given :-

An  object starting from rest travels 20 metres in the first 2 seconds,and 100 metres in the next 10 seconds .

To Find :-

Velocity after 7 sec

Solution :-

We know that

s = ut + 1/2 × at²

20 = (0)(2) + 1/2 × a × (2)²

20 = 0 + 1/2 × a × 4

20 = 2a

20/2 = a

10 = a

Now

v² = u² + 2as

v² = (0)² + 2(10)(20)

v² = 0 + 20 × 20

v² = 400

v = √400

v = 20 m/s

Now

After 2 seconds

v = u

s = ut + 1/2 at²

100 = (20)(10) + 1/2 × a × (10)²

100 = 200 + 1/2 × a × 100

100 = 200 + 50a

100 - 200 = 50a

-100 = 50a

-100/50 = a

-2  = a

Now

v = u + at

v = 20 + (-2)(7)

v = 20 + (-14)

v = 20 - 14

v = 6 m/s