Chapter 9: Force and Laws of Motion - Physics 30 Numerical Problems

Introduction:
In Chapter 9 of Class 9 Physics, we delve into the concepts of force and laws of motion. This chapter introduces us to various numerical problems based on these principles. Let's explore some of these numerical problems in detail.

1. Problem:
A car of mass 1200 kg is moving with a velocity of 20 m/s. The driver applies the brakes, and the car comes to rest in 4 seconds. Calculate the retardation and the force applied by the brakes.

Solution:
Given:
Mass of the car (m) = 1200 kg
Initial velocity (u) = 20 m/s
Final velocity (v) = 0 m/s
Time taken (t) = 4 s

Step 1: Calculate the acceleration using the formula:
Acceleration (a) = (v - u) / t
a = (0 - 20) / 4 = -5 m/s² (negative sign indicates retardation)

Step 2: Calculate the force using Newton's second law of motion:
Force (F) = mass (m) * acceleration (a)
F = 1200 kg * (-5 m/s²) = -6000 N

Therefore, the retardation is -5 m/s², and the force applied by the brakes is -6000 N (negative sign indicates the opposite direction to the motion).

2. Problem:
A 10 kg object is pushed with a force of 50 N resulting in an acceleration of 5 m/s². Calculate the frictional force acting on the object.

Solution:
Given:
Mass of the object (m) = 10 kg
Applied force (F) = 50 N
Acceleration (a) = 5 m/s²

Step 1: Calculate the net force using Newton's second law of motion:
Net force (F_net) = mass (m) * acceleration (a)
F_net = 10 kg * 5 m/s² = 50 N

Step 2: Calculate the frictional force:
Frictional force (F_friction) = Applied force (F) - Net force (F_net)
F_friction = 50 N - 50 N = 0 N

Therefore, the frictional force acting on the object is 0 N.

Conclusion:
In this chapter, we encountered two numerical problems related to force and laws of motion. By applying the appropriate formulas and equations, we were able to calculate the retardation and force applied by the brakes in the first problem and determine the frictional force in the second problem. Understanding these numerical problems helps in strengthening our grasp of the concepts of force and laws of motion.

In local force is a pull or a push; but in brief it is inertia that remain same and do not change for change we need a motion called force