Important Questions for Class 9 Science Chapter 8

Important Questions for Class 9 Science Chapter 8 Force And Laws of Motion बल तथा गति के नियम

Question 1:
For how long should a force of 100N acts on a resting body of 20 kg so that it acquires a velocity of 100 ms⁻¹.
100 N का बल 20 kg के एक विरामावस्था पिंड पर कितने समय तक लगाया जाए ताकि वह 100 ms⁻¹ का वेग प्राप्त कर ले?

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Question 2:
An automobile vehicle has a mass of 1500 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.7 ms⁻²?
एक गाड़ी का द्रव्यमान 1500 kg है। यदि गाड़ी को 1.7 ms⁻² के ऋणात्मक त्वरण के साथ विरामावस्था में लाना है। तो गाड़ी तथा सड़क के बीच लगने वाला बल कितना होगा?
Answer
Using Newton’s second law of motion, F = m \(\times\)a
Here, m = 1500 kg, a = – 1.7 ms⁻²
So, F = 1500 \(\times\) (- 1.7) = – 2550 N

Question 3:
How does a karate player breaks a slab of ice with a single blow?
एक कराटे खिलाड़ी एक ही झटके से बर्फ की सिल्ली को कैसे तोड़ देता है?

Question 4:
Why do you think it is necessary to fasten your seat belts while travelling in your vehicle?
आप अपने वाहन में यात्रा करते समय सीट बेल्ट बांधना क्यों आवश्यक समझते है?
Or
Why is it advised to wear seat belt in the car while driving?
यात्रा के समय कार में सीट बेल्ट बांधने की सलाह क्यों दी जाती है?

Question 5:
Why does an athlete puts some sands or cushion on the ground while high jumping?
ऊंची कूद लगाते समय एक एथलिट जमीन पर कुछ रेत या गद्दे क्यों रखता है?

Question 6:
A force of 5 N produces an acceleration of 8 m s^–2 on a mass m, and an acceleration of 24 m s^-2 on mass m₂. What acceleration would the same force provide if both the masses are tied together?

Question 7:
Define inertia.
जड़त्व को परिभाषित कीजिए।

Question 8:
Give three examples of situations from your surroundings that can be explained by first law of motion.

Question 9:
If two person pushing a box from opposite directions with same magnitude, as shown will the box move or not? Explain.

Question 10:
State second law of motion also write its mathematical expression.

Question 11:
A train is moving with a velocity of 54 km/h and it takes 2 s to stop after the brakes are applied. Calculate the force exerted by the brakes on the train. (Mass of the train is 800 kg).

Question 12:
What is the momentum of a body of mass 200 g moving with a velocity of 15 m s^-1.

Question 13:
A body of mass 5 kg starts and rolls down 32 m of an inclined place is 4 s. Find the force acting on the body?

Question 14:
Can an object have mechanical energy even if its momentum is zero? Justify your answer.
क्या किसी वस्तु में संवेग शून्य होने पर भी यांत्रिक ऊर्जा हो सकती है? अपने उत्तर का औचित्य बताइए।
Answer
Yes, an object can have mechanical energy even if its momentum is zero.
For example, a stone kept at a height has potential energy due to its position above the ground. At that moment, the stone is at rest, so its velocity and momentum are zero, but it still possesses mechanical energy in the form of potential energy.
हाँ, किसी वस्तु में संवेग शून्य होने पर भी यांत्रिक ऊर्जा हो सकती है।
उदाहरण के लिए, ऊँचाई पर रखी हुई पत्थर की वस्तु विराम अवस्था में होती है, इसलिए उसका वेग और संवेग शून्य होता है, फिर भी उसमें अपनी स्थिति के कारण स्थितिज ऊर्जा होती है। अतः उसमें यांत्रिक ऊर्जा मौजूद होती है।