Question

A rally driver has 5s to stop her car, which is travelling
at a speed of 20m/s. What is her average retardation?​​

Answer 1

Given:-

• Initial velocity of car (u) = 20m/s

• Final velocity of car (v) = 0m/s

• Time taken (t) = 5s

To Find:-

• Retardation of car (a).

Solution:-

By using 1st equation of motion

⟹ v= u+at

Put the values, we get

⟹ 0= 20 + a× 5

⟹ -20 = a× 5

⟹ a = -20/5

⟹ a = -4m/s²

∴ The retardation of the car is -4m/s².

Additional Information!!

✧ The rate of change of velocity at per unit time is called acceleration .

✧ Negative acceleration is called retardation

✧ SI unit of acceleration is m/s²

✧ It is vector Quantity ( both magnitude and direction).

Answer 2

⭐ GIVEN :-

☆ Initial Velocity = 0m/s

☆ Final Velocity = 20m/s

☆ Time taken = 5 seconds.

⭐ TO FIND :-

☆ Retardation.

⭐ SOLUTION :-

We can use First Equation of Motion.

v = u + at.

Put the values.

➠ 0 = 20 + 5a.

➠ 5a = -20.

➠ a = -20/5.

➠ a = -4m/s²

Hence, The Retardation = -4m/s².

ADDITIONAL INFORMATION :-

• Acceleration is the rate of change of Velocity.

• Retardation is the negative acceleration.

• The SI unit of Acceleration = m/s².

• It is a Vector Quantity.