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Numerical Problems (Solved): Force and Newton's Law of Motion | Science Class 9 PDF Download

Q1: A cricket ball of mass 70 g moving with a velocity of 0.5 m s-1 is stopped by player in 0.5 s. What is the force applied by player to stop the ball?  
Sol. Here m = 70 g = 0.070 kg; u = 0.5 m s-1; v = 0; t = 0.5 s 
Numerical Problems (Solved): Force and Newton`s Law of Motion | Science Class 9

Q2: What will be acceleration of a body of mass 5 kg if a force of 200 N is applied to it?  
Sol. Here m = 5 kg; F = 200 N 
 F = ma or a = F/m 

Numerical Problems (Solved): Force and Newton`s Law of Motion | Science Class 9 

Q3: A bullet of mass 10 g is fired from a rifle. The bullet takes 0.003 s to move through its barrel and leaves with a velocity of 300 ms-1. What is the force exerted on the bullet by the rifle?  
Sol. Here m = 10 g = 0.010 kg ; u = a ; v = 300 m s-1 
 t = 0.003 s, F = ? 

Numerical Problems (Solved): Force and Newton`s Law of Motion | Science Class 9

Q4: What force would be needed to produce an acceleration of 1 ms-2 on a ball of mass 1 kg?  
Sol. Here m = 1 kg; a = 1 ms-2 ; F = ? 
 Now F = m a = 1 × 1 
 or F = 1 newton.
 

Q5: What is the acceleration produced by a force of 5 N exerted on an object of mass 10 kg?  
Sol. Here F = 5 N; m = 10 kg; a = ? 
 Now F = ma o
 a = 0.5 ms-2 
 

Q6: How long should a force of 100 N act on a body of 20 kg so that it acquires a velocity of 100 ms-1 
Sol. Here v _ u = 100 m s-1, m = 20 kg; F = 100 N ;t = ? 
We know 

Numerical Problems (Solved): Force and Newton`s Law of Motion | Science Class 9

Q7: Which would require greater force: accelerating a 10 g mass at 5 m s_2 or 20 g mass at 2 m s-2 
Sol. In first case m1 = 10 g = kg = 0.010 kg; 
 Now a1 = 5 ms-2 ; F1 = ? 
 F1 = m1a1 = 0.010 × 5
 F1 = 0.050 newton 
 In second case, m2 = 20 g =0.020 kg 
 or m2 = 0.020 kg 
 a2 = 2 m s-2 ; F2 = ? 
 Now F2 = m2a2 = 0.020 × 2 
 or F2 = 0.04 newton 
 We find that F1 > F2, hence more force is required to accelerate 10 g at 5 m s-2 than accelerating 20 g at 2 ms-2.  

Q8: A force of 5 N gives a mass m1, an acceleration of 8 ms-2 and a mass m2, an acceleration of 24 m s-2. What acceleration would it give if both the masses are tied together?  
Sol. Let us first find mass m1 and m2. 
F = m1 a1 
5 =m1 (8) or m1 = 5/8 kg 
F = m2 a2 
5 = m2 (24) or m2 = 5/24 kg 
Total mass M = m+ m2 

Numerical Problems (Solved): Force and Newton`s Law of Motion | Science Class 9

Let A be the acceleration produced in mass M. 
F = MA 

Numerical Problems (Solved): Force and Newton`s Law of Motion | Science Class 9

Hence the acceleration of the combination is 6 ms-2

Q9: If 1000 N force is required to accelerate an object to the rate of 5m/s2, what will be the weight of the object?

Sol: According to question 

Numerical Problems (Solved): Force and Newton`s Law of Motion | Science Class 9

Q10: After applying a force of 1000 N an object of mass 2000 kg will achieve what acceleration?

Sol: 

Numerical Problems (Solved): Force and Newton`s Law of Motion | Science Class 9

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FAQs on Numerical Problems (Solved): Force and Newton's Law of Motion - Science Class 9

1. What is the relationship between force and Newton's Law of Motion?
Ans. According to Newton's Law of Motion, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This means that the greater the force applied to an object, the greater its acceleration will be.
2. How can you calculate the force acting on an object?
Ans. The force acting on an object can be calculated using the formula: Force = mass x acceleration. This formula is derived from Newton's second law of motion, which states that force is equal to mass times acceleration.
3. What are the different types of forces that can act on an object?
Ans. Some of the different types of forces that can act on an object include gravitational force, frictional force, normal force, tension force, and applied force. Each of these forces can affect the motion of an object in different ways.
4. How does Newton's third law of motion relate to force?
Ans. Newton's third law of motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal force in the opposite direction. This principle helps explain how forces interact between objects.
5. Can a force act on an object without causing it to accelerate?
Ans. Yes, a force can act on an object without causing it to accelerate if there is an equal and opposite force acting on the object. In this case, the forces would be balanced, resulting in no net acceleration of the object.
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