Second Law of motion for class 9th(lec 3)

 video lectures for Second Laws of motion

Question 1:  newton = _____ dyne.

a) `10^{4}`

b) `10^{5}`

c) `10^{6}`

d) `10^{10}`

Question 2: The impulse of a body is equal to _____.

a) momentum change

b) Rate of change of its momentum

c) impulse

d) none of above

Question 3: `1 kgwt` is equal to ________`N`.

a) `9.8 N`

b) `8.9 N`

c) `0.9 N`

d) `0.8 N`

Question 4: A car moving at a speed of `36 kmh^{-1}` is brought to rest while covering a distance of `100 m`. If the mass of the car is `400 kg`, find the retarding force on the car and the time taken by the car to stop.

a) `200N` 

b) `400N`

c) `-200N`

d) `-100N`

Question 5: A coconut of mass  `1 kg` falls from a tree. Find its weight (Take acceleration due to gravity = `9.8 ms^{-2}`)

a) `9.8 N`

b) `98 N`

c) `0.98 N`

d) `0.8 N`

Question 6: A tennis player returns, with his racket, a tennis ball of mass `100 g` coming towards him with a speed of `162 kmh^{-1}`. If the ball returns with the same speed and it remains in contact with racket for `0.1 s`, find the force exerted by him on the ball.

a) `60 N`

b) `-60 N`

c) `-90 N`

d) `90 N`

Question 7: A lorry moving with `54 kmh^{-1}` speed hits a rock and comes to halt within `0.1 s`. If the mass of the lorry is twenty metric tonne, then find the force exerted by the rock on the lorry.

a) `3\times10^{6}M`

b) `-3\times10^{6}M`

c) `3\times10^{-6}M`

d) `3\times10^{-6}M`

Question 8: What is normal reaction or normal force?

Question 9: The impulse of a body is equal to _____.

Question 10: A football of mass `0.5 kg` moving with a velocity of `10 ms^{-1}` hits a pole and, the ball turns back and moves with a velocity of `20 ms^{-1}`. Find the impulse and the force exerted on the ball if the force acts for `0.02 s`.

a) `7.5kgms^{-1}`

b) `7.5kgms`

c) `0.75kgms^{-1}`

d) `0kgms^{-1}`

Question 11: Derive `F` = `ma` from Newton’s second law of motion

Question 12: The mass of a body is `20 kg`. This weight is equal

to _____.

(a) `1960 N`  

(b) `196 J`

(3) `196\times10^{5}dyan` 

(d) `19.6 N`

Question 13: The force acting on a body when its momentum changes by

`10 kg ms^{-1}`, in `5 sec` is _____ `N`.

(a) `15`  

(b) `2`

(c) `5`  

(d) `10`

Question 14: The change in momentum of a body (a) is equal to the force applied on it. (b) is equal to the product of force applied on it and the time of application of the force. (c) Both (a) and (b) are true (d) Both (a) and (b) are false

Question 15: The rate of change in momentum of a body is

(a) equal to the force applied on it.

(b) proportional to the force applied on it.

(c) in the direction of applied force.

(d) All the above are true

Question 16: A body `‘A’` of mass `4kg` on collision exerts a force on

another body `'B'` of mass `10kg`. If the acceleration produced in `B` is `10 ms^{-2}`, then the acceleration (in magnitude) of `A` is ______.

(a) `25 ms^{-2}`  

(b) `10 ms^{-2}`

(c) `52 ms^{-2}`  

(d) `5 ms^{-2}`

Answer Key

Q1. (b), Q2. (a), Q3. (a), Q4. (c), Q5. (a), Q6. (c), Q7. (a),

Q8. The normal force is defined as the force that a surface employs on any other body. If that body is at rest, it means that the net force acting on the body is equal to zero. This means that the downward force, that is, the weight, must be similar to the upward force, which is the normal force.,

Q9. Change in momentum

Q10. (a),

Q11. the force F acting on a body is equal to the mass m of the body multiplied by the acceleration an of its center of mass.

Q12. (c), Q13. (b), Q14. (b), Q15. (d), Q16. (a),