Question

A car moving with a speed of 72 km/hr comes to rest after 4son applying brake. If mass of the car including passengers is 1000 kg, what will be the force applied when brake is operated?

Answer 1

Given :

• Initial velocity (u) = 72 km/h = 20 m/s
• Final velocity (v) = 0 m/s (as it applies brakes)
• Time (t) = 4 seconds
• Mass (m) = 1000 kg

To find :

• Force applied

According to the question,

By using Newtons first equation of motion,

→ v = u + at

Where,

• v = Final velocity
• u = Initial velocity
• a = Acceleration
• t = Time

→ Substituting the values,

→ 0 = 20 + a × 4

→ 0 - 20 = 4a

→ - 20 = 4a

→ - 20 ÷ 4 = a

→ - 5 = a

So,the acceleration is -5 m/s².

Note : Negative signs means retardation.

Now,

→ Force = Mass × Acceleration

Or,

→ F = ma

→ Substituting the values,

→ F = 1000 × (-5)

→ F = - 5000 N

So,the force is - 5000 Newton.

Note : Negative signs means that the force is in opposite direction.

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