Question

A motor cycle moving with 72km/hr is applied brake and it accelerates with an negative accn 5ms^-2 and stops.how long will he apply the brake? find the distance covered just before stopping.​

Answer 1

Required Answer :

• The brake will be applied for 4 seconds
• The distance covered just before stopping = 40 m

Given :

• Initial velocity = 72 km/h
• Final velocity = 0 m/s
• Acceleration = 5 m/s²

To find :

• How long will be the brake applied
• Distance covered just before stopping

Solution :

Firstly, let's convert the initial velocity from km/h into m/s. For that, multiply the value by 5/18.

Final velocity :

⇒ Final velocity = 72 × 5/18

⇒ Final velocity = 4 × 5

⇒ Final velocity = 20 m/s

Using first equation of motion,

First equation of motion :

• v = u + at

where,

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

Substituting the given values :

⇒ 20 = 0 + (5)(t)

⇒ 20 = 5 × t

⇒ 20/5 = t

⇒ 4 = t

Time = 4 seconds

Therefore,

• The brake will be applied for 4 seconds

Using third equation of motion,

Third equation of motion,

• v² - u² = 2as

where,

• v denotes the final velocity
• u denotes the initial velocity
• a denotes the acceleration
• s denotes the distance

Substituting the given values :

⇒ (20)² - (0)² = 2(5)(s)

⇒ 400 = 10 × s

⇒ 400/10 = s

⇒ 40 = s

Distance = 40 m

Therefore,

• The distance covered just before stopping = 40 m