Test: Newton's Second Law Of Motion - Class 9 MCQ

Force is the product of the ass and acceleration.
Therefore, Force = Mass x Acceleration 
The SI unit of Force is  kg.m/s² or Newton
1 Newton =  10⁵ Dyne

To find the time taken for the body to come to rest, we can use the formula derived from Newton's second law:

F=ma

where:

• F is the force applied,
• m is the mass of the body,
• a is the acceleration.

First, we calculate the acceleration:

The body is initially moving with a velocity of 10 m/s and will come to rest, so the final velocity v=0v = 0v=0.

Using the equation of motion:

v=u+at

where:

• v is the final velocity (0 m/s),
• u is the initial velocity (10 m/s),
• a is the acceleration (-0.25 m/s²) (negative because the force is acting opposite to the direction of motion),
• t is the time taken.

Substitute the values:

0=10+(−0.25)t

0.25t=10

So, the time taken by the body to come to rest is 40 seconds.

Answer: 3 (40 s)

The relationship also implies the conservative of momentum : when the net force on the body is zero, the momentum of the body is constant. Any net force is equal to the rate of change of the momentum.

For the same force, an object with twice the mass will have half the acceleration. If it had three times the mass, the same force will produce one-third the acceleration. Four times the mass gives one-fourth of the acceleration, and so on.
This type of relationship between quantities (double one, get half the other) is called an inverse proportion or inverse variation. In other words, then:
The acceleration is inversely proportional to the mass of the object.
Newton's Second Law
"If the net force on an object is not zero, the object will accelerate. The direction of the acceleration is the same as the direction of the net force. The magnitude of the acceleration is directly proportional to the net force applied, and inversely proportional to the mass of the object."

Force can be calculated from Newton’s second law of motion which gives that force is the product of mass and acceleration.

In a high jump athletic event, the athletes are made to fall either on a cushioned bed or sand bed. This is to increase the time that the athletes fall to stop after making the jump. This decreases the rate of change of momentum and hence the force. As a result, the athlete does not get injured.

Change in momentum = mv - mu
When m = 7000kg, v= 200m/s, u = 100 m/s
Now, 700 * 200 - 700 x 100 = 140000 - 70000 = 70000 kg. m/s

We know , p=mv Here m=0.5 kg & v=10 m/s . So p=0.5*10=5 Kg m/s

We know; P = mv
If m = 2 m ;   v= v/2
P  =  (2m) (v/2) 
P = mv