Question

An object starting from rest travels 20 m in first 2 seconds and 160 m in next 4 seconds. Find the velocity 7 seconds from the start.​

Answer 1

Answer:

intial velocity u=0m/s

time=2s

travelled distance = 20m

let accelaration is a

principle:

S=ut+½at²

20=1/2*a*4

a=10m/s²

Distance travelled in first 7 seconds

=1/2*10*49

=245m

Answer 2

Answer:

➤ Given:

• Initial velocity (u) = 0
• Distance (s) = 20 m
• Time (t) = 2 sec.

➤ To find:

Velocity 7 seconds from the start.

➤ Solution:

In order to find the velocity at the end of 2 sec firstly find the acceleration.

As we know that,

S = ut + 1/2at²

where S is distance covered, ‘u’ is initial velocity, ‘t’ is time taken and ‘a’ is acceleration.

➪ 20 = 0 + 1/2a × 4

➪ a = 20 m/s².

Now velocity

v = u + at

➪ v = 10 × 2

➪ v = 20 m/s.

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Now after 4 sec,

• Initial velocity (u) = 20 m/s
• Distance (s) = 260 m
• Time (t) = 4 sec

Assume the acceleration be a₁.

Now by again using the formula of S = ut + 1/2at²

160 = 20 × 4 + 1/2a1 × 16

➪ a₁= 10 m/s².

Now velocity after 4 seconds =

v = u + at

➪ v = 0 + 10 × 7

➪ v = 70 m/s.

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