Question

a bicycle was travelling at 20m/s when it applied brakes and deaccelerated at the rate of 5m/s².How long will it take before it becomes stop​

Answer 1

Answer:

4 seconds

Explanation:

As per the provided information in the given question, we have :

• Initial velocity of the bicycle (u) = 20 m/s
• Retardation = 5 m/s² (So, acceleration = –5 m/s²)
• Final velocity (v) = 0 (as it comes to stop)

We are asked to calculate how long will it take before it becomes stop.

By using the first equation of motion,

$\longmapsto \bf {v = u + at }$

• v denotes final velocity
• u denotes initial velocity
• a denotes acceleration
• t denotes time

Substituting values,

$\longmapsto \rm {0 = 20 + (-5)t }$

$\longmapsto \rm {0 = 20 -5t }$

$\longmapsto \rm {0 -20 = -5t }$

$\longmapsto \rm { -20 = -5t }$

$\longmapsto \rm {\cancel{\dfrac{-20}{-5}} = t }$

$\longmapsto \bf { 4 \; s = t }$

∴ It'll take 4 seconds to come to stop.

$\rule{200}2$

Points to remember :

Equations of motion :

$\boxed{ \begin{array}{cc} \pmb{\sf{ \quad \: v = u + at \quad}} \\ \\ \pmb{\sf{ \quad \: s= ut + \cfrac{1}{2}a{t}^{2} \quad \: } } \\ \\ \pmb{\sf{ \quad \: {v}^{2} - {u}^{2} = 2as \quad \:}}\end{array}}$

• v denotes final velocity
• u denotes initial velocity
• a denotes acceleration
• t denotes time
• s denotes distance

• When body starts from rest, its initial velocity is 0.
• When body comes to rest, its final velocity is 0.

Answer 2

Answer:-

• Initial velocity=u=20m/s
• Final velocity=v=0m/s
• Acceleration=a=-5m/s^2
• Time=t=?

We know that

$\boxed{\sf a=\dfrac{v-u}{t}}$

$\\ \sf\longmapsto t=\dfrac{v-u}{a}$

$\\ \sf\longmapsto t=\dfrac{0-20}{-5}$

$\\ \sf\longmapsto t=\dfrac{-20}{-5}$

$\\ \sf\longmapsto t=4s$