Question

9. A car advertisement states that a certain car can accelerate from rest to 70 km/h in 7 seconds. Find the car’s average acceleration.

Answer 1

Answer:

final velocity= 19.44 m/s

acceleration= (19.44-0)/7

=19.44/7 = 2.78 m/s^2

Answer 2

Given :

Initial velocity = zero (i.e., at rest)

Final velocity = 70 km/hr

Time interval = 7s

To Find :

Average acceleration of the car$.$

Solution :

❒ Acceleration is measured as the rate of change of velocity.

• It is a vector quantity having both magnitude as well as direction.
• It can be positive, negative or zero.
• SI unit : m/s
• CGS unit : cm/s
• Dimension formula : [L¹T‾²]

As per first equation of kinematics;

$\sf:\implies\:v=u+at$

» v denotes final velocity

» u denotes initial velocity

» a denotes acceleration

» t denotes time

Conversion : 1 km/hr = 5/18 m/s

∴ 70 km/hr = 70 × 5/18 = 19.44 m/s

By substituting the given values;

➙ v = u + at

➙ 19.44 = 0 + (a × 7)

➙ a = 19.44/7

➙ a = 2.78 m/s²