HOTS Questions: Forces & Laws of Motion - Class 9 MCQ

1) A cart is pulled by the horse as the horse applies a force on earth and earth applies a equal and opposite force. this is stated in Newton third law of motion.
2) We get a backward jerk due to inertia as the car speeds up and our body tends to move backwards and resist the change.
3) Sole of shoe worns out due to friction.
4) The spring in the gun transfers the momentum to the bulletand according to law of conservation of momentum the gun recoils.

This is because when we hit a carpet the carpet starts moving forward and its inertia of rest changes into the inertia of motion but the dust particles which are there with the carpet they move just because of the carpet but actually the particles remain at rest that is why these particles fall of due to the change of inertia.

Newton's third law states that for every action, there is an equal and opposite reaction. This means that the forces are equal in magnitude (1), act simultaneously (3), and are opposite in direction (4). However, they act on different bodies, not the same one.

If an object experience a net zero unbalanced force, than the body moves with constant velocity. Zero unbalanced force due to produce acceleration in the body.

D is the correct option.Force is the cause of acceleration. Mass Is the quantitative measure Of inertia. We apply powder on the carrom board to decrease friction. Tyres of vehicles made rough to increase friction.

Force = 7 kg-wt = 7×10 = 70 N, mass = 10 kg. therefore, acceleration produced in the body = F/a = 70/10 
= 7 ms^-2.

Newton’s third law states that for every action (force) in nature there is an equal and opposite reaction. In other words, if object A exerts a force on object B, then object B also exerts an equal and opposite force on object A.

For every action, there is an equal and opposite reaction. The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object.

The objects interact. The action and reaction force always act on different objects. Two forces acting on the same object, even if they have the same magnitude and point in opposite directions, never form an action-reaction pair.

A passenger falls backward when a bus suddenly start moving in the forward direction due inertia of rest. A gun recoils backward with small speed than the bullet moving forward due to law of conservation of momentum.

D is the correct option.A force acting on an object causes the object to change its shape or size, to start moving, to stop moving, to accelerate or decelerate. When there's the interaction between two objects they exert a force on each other, these exerted forces are equal in size but opposite in direction.

Force is the equal to the rate of change of momentum. Force = final momentum-initial momentum/time , f = mv-mu/t.

To reduce the friction, oiling between contact surface, using ball bearing and using grease between contact surfaces. Making scratches between contact surfaces increase the friction.

Answer:
The instruments that make our work easier are called machines. Machines are tools or devices that are designed to perform specific tasks or functions. They are created to simplify and automate various processes, making work more efficient and less labor-intensive. Here are some key points to consider:
- Definition: Machines are mechanical or electrical devices that use energy to perform work. They can be simple, such as a lever or a pulley, or complex, like a computer or a car.
- Types: There are various types of machines, each designed for a specific purpose. Some common examples include generators, motors, and electric currents. However, it is important to note that these are specific types of machines, and the term "machine" itself is a more general term.
- Function: Machines are used to make work easier by reducing the amount of force, energy, or time required to complete a task. They can increase productivity, improve precision, and enable humans to perform tasks that would otherwise be impossible or extremely difficult.
- Examples: Machines can be found in almost every aspect of our daily lives. Some common examples include cars, computers, washing machines, elevators, and power tools. These machines have revolutionized industries and have greatly enhanced our quality of life.
- Importance: Machines have had a profound impact on society, driving technological advancements and shaping the way we live and work. They have played a crucial role in industrialization, automation, and the development of new industries.
In conclusion, machines are the instruments that make our work easier. They are designed to perform specific tasks or functions, using energy to simplify and automate various processes. From simple tools to complex devices, machines have revolutionized industries and greatly enhanced our quality of life.

Newton’s second law of motion states that rate of change in momentum is equal to force applied. Momentum is the product of mass and velocity. So, mass, velocity and time all are associated with Newton’s second law of motion.

Momentum of a body is equal to product of mass and velocity. Momentum​

The correct option is Option C.
This is because when acceleration increases so will speed and velocity. As acceleration is a type of accelerated force a force will always act on the body.

The force can be measured by newton’s second law of motion. First law of motion states that object in rest or uniform motion tends to remain in its state.

Internal forces are those forces which exert on each other when the bodies are part of the system. The forces acting between the atoms of molecules that keep them together are example of internal force.

When a moving bus at high speed suddenly stops, the passenger feels jerk in forwarding direction due to the inertia of motion, which tends to keep the moving body in motion.

If no unbalance force acts on the body, the speed of body remain constant. So, a body moving with constant speed of 5m/s does not have any unbalanced force acting on it.

The weight of the body is the measure of force by which object is attracted towards the centre of earth. It always acts vertically downwards.

F₁= mass of car x acceleration produced in the car =m₁*a₁
F₂= mass of bus x acceleration produced in the bus =m₂*a₂
m₂/m₁= 1:50
since F₁= F₂
m₁*a₁ =m₂*a₂
a₁/a₂ =m₂/m 
          =1:50