Question

A truck is moving with speed of 54 km/h. Truck’s driver applied brakes suddenly and brings the truck to rest in 5 sec. What is the average retarding force on truck, if the mass of the truck and driver is 400 kg?

Answer 1

Answer

• Retarding force on truck is " 1200 Newtons "

Given

• A truck is moving with speed of 54 km/h. Truck’s driver applied brakes suddenly and brings the truck to rest in 5 sec

To Find

• Average retarding force on truck, if the mass of the truck and driver is 400 kg

Formula Used

• 1st equation of motion

• v = u + at

• Newton Second's Law
• F = ma

Solution

Initial velocity , u = 54 km/h = 54 × ⁵/₁₈ m/s = 15 m/s

Final velocity , v = 0 m/s [ ∵ Finally goes to rest ]

Time , t = 5 s

Acceleration , a = ? m/s²

Apply 1st equation of motion .

⇒ v = u + at

⇒ 0 = 15 + a(5)

⇒ 5a = - 15

⇒ a = - 3 m/s²

- ve sign denotes retardation , which is opposite to acceleration .

Mass , m = 400 kg

Acceleration , a = - 3 m/s²

A/c Newton's Second Law ,

⇒ F = ma

⇒ F = 400 × - 3

⇒ F = - 1200 N