Question

what is ans for these ques

Answer 1

Explanation:

First answer is available in your Class 9 text book probably. Check it.

1.b.

If unbalanced force is zero and mass is m then we have the following formula,

F=ma

or,0=ma

or,a=0

or,(v-u)/t=0

or,v=u

Hence, in the absence of any balanced force an object remains in the state of rest or in a state of uniform motion.(Proof of 2nd law using first law)

2.

find the slope of the given graph you will get

a=v-u/t

or,a=30-10/20=1 m/s^2

now find the accelerating Force for the given mass

F=20×1=20 N

3. Boxer moves his/her head backwards so that the punch of his/her opponent takes much longer time to reach to his face .As the time increases the rate of change of momentum decreases which decreases the force and its effect.