Question

A truck travelling at 54 km/h is slow down to 36 km/h in 10 sec. Find the retardation​

Answer 1

Given :–

• Initial speed (u) = 54 km/hr
• Final speed (v) = 36 km/hr
• Time (t) = 10s

To Find :–

• The retardation.

Solution :–

Given,

• u = 54 km/hr
• v = 36 km/hr
• t = 10s

First, we need to convert u and v to km/hr into m/s.

For converting, we multiply $\dfrac{5}{18}$ by the value of km/hr.

So,

Initial speed (u) = $\cancel{54} \times \dfrac{5}{\cancel{18}}$

⟹ $\cancel{27} \times \dfrac{5}{\cancel{9}}$

⟹ $\cancel{9} \times \dfrac{5}{\cancel{3}}$

⟹ 3 × 5

⟹ 15 m/s

• u = 15 m/s

Now,

Final speed (v) = $\cancel{36} \times \dfrac{5}{18}$

⟹ $\cancel{18} \times \dfrac{5}{\cancel{9}}$

⟹ $\cancel{6} \times \dfrac{5}{\cancel3}$

⟹ 2 × 5

⟹ 10 m/s

• v = 10 m/s

Now,

We have,

• u = 15 m/s
• v = 10 m/s
• t = 10s

Retardation = $\dfrac{v - u}{t}$

⟹ $\dfrac{10 - 15}{10}$

⟹ $\dfrac{-5}{10}$

⟹ –0.5 m/s²

Answer 2

Gɪᴠᴇɴ :-

• Initial velocity (u) = 54km/h
• Final velocity (v) = 36 km/h
• Time taken (t) = 10s

ᴛᴏ ғɪɴᴅ :-

• Retardation

sᴏʟᴜᴛɪᴏɴ :-

➭ Initial velocity = 54km/h

→ u = 54 × 5/18

→ u = 15m/s

➭ Final velocity = 36km/h

→ v = 36 × 5/18

→ v = 10m/s

According to the first equation of motion

→ v = u + at

→ 10 = 15 + a × 10

→ 10 - 15 = 10a

→ 10a = - 5

→ a = -10/5 = - 2m/s

➭ Minus shows retardation

Hence,

• Retardation of truck is 2m/s²