Question

An object starting from rest travels 20 m in first 2 s and 160 m in next 4 s. What will be the velocity after 7 s from the start?​

Answer 1

Answer:

The velocity after 7 s from the start will be 70 m/s.

Explanation:

In first 2 seconds, the initial velocity (u) = 0

distance (s) = 20 m

and time (t) = 2 s

Now, we know that S = ut + 1/2 at$^{2}$

where S is distance

u is initial velocity

a is acceleration

and t is time.

By substituting the known values, we get

→ 20 = 0 + 1/2 a × 4

→ a = 10 m/s$^{2}$

We will find the velocity at the end of two second using Newton's first law of motion i.e. v = u + at

v = u + at

→ v = 10 × 2

→ v = 20 m/s

Now, in next four second

S = ut + 1/2 at$^{2}$

By substituting the known values, we get

160 = 20 × 4 + 1/2 ${a_1}$ × 16

→ 80 = ${a_1}$

→ ${a_1}$ = 20 m/s$^{2}$

Acceleration is constant/uniform in both the motion.

Now, again using Newton's first law

v = u + at

→ v = 0 + 10 × 7

→ v = 70 m/s

Thus, the velocity after 7 s from the start is 70 m/s.