Question

A car of mass 2000 kg changes its speed from 72 km/h to 36 km/h in 5 second. The force applied by its brake is

Answer 1

Gɪᴠᴇɴ :-

• Mass (m) = 2000 kg
• Initial velocity (u) = 72 ×5/18 = 20m/s
• Final velocity (v) = 36×5/18 = 10 m/s

ᴛᴏ ғɪɴᴅ :-

• Force (F) applied by brakes

sᴏʟᴜᴛɪᴏɴ :-

On using 1st equation of motion, we get,

➦ v = u + at

→ 10 = 20 + a × 5

→ 10 - 20 = 5a

→ 5a = -10

→ a = -10/5

→ a = -2 m/s²

Hence,

• Acceleration (a) = 2 m/s²

Negative sign shows deceleration or retardation

Now,

We know that,

➦ Force = Mass × Acceleration

➦ F = ma

➦ F = 2000 × -2

➦ F = -4000 N

Hence,

• Force (F) applied by brakes is 4000 N

Negative sign shows that force must be applied in opposite direction of motion .

Answer 2

4000 N is the force applied by its brake on a car of mass 2000kg changes its speed from 72 km/h to 36km/h in 5 seconds

Explanation:

Initial Speed = 72 km/hr =  72 * 5 /18  = 20 m/s

Final Speed = 36 km/hr =  36 * 5/18  = 10 m/s

acceleration = Change in Velocity / time

=> acceleration =  ( 10 - 20)/5

=>  acceleration =  -10/5

=>  acceleration =  -2 m/s²

Hence there is a deceleration of 2 m/s² due to force applied by break

force applied by its brake = mass * acceleration

=> 2000 * 2

= 4000 N

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