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Why athletes stop themselves before the line marked for javelin throw
(A) Due to inertia of rest
(B) Due to inertia of motion
(C) Due to inertia of direction
(D) All

Last updated date: 20th Jun 2024
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Hint An object in motion will tend to remain in motion according to Newton’s first law. While running forward an athlete must not cross the marked line or it will be regarded as foul.

Complete step by step answer
According to Newton’s first law of motion, an object at rest tends to remain at rest and an object in uniform motion tends to remain in uniform motion unless acted upon by an external force. This is known as the inertial law. Uniform motion means that the object is moving at a constant speed. When forces are applied, the object will either accelerate or decelerate depending on the direction of the applied force relative to the direction of the initial motion. If the force was applied in the same direction as the motion, the body accelerated, otherwise the body decelerated.
The Inertial of a body is divided into three parts, they are
Inertia of rest: this is the tendency of the body to remain at a state of rest. It is also described as the tendency of the body to oppose any change of state of rest or the tendency of the body to resist motion.
Inertia of motion; this is the tendency of a body to remain in the state of motion. It can also be described as the tendency of a body to resist the change in the state of motion of the body.
Inertia of direction: the tendency of a body to remain in a particular direction. It can also be described as the resistance to a change in direction
For a javelinist running on a straight line, who wants to stop before crossing the foul line hence must stop themselves before the mark due to the fact that an inertia of motion tends to keep them moving forward before actually coming to rest.
Hence, the correct option is B.

An application of the inertia of motion is sometimes seen in electric cars. Usually to break (apply break in) a car is to convert all its kinetic energy to heat by generating large friction between the tyres and the road through the breaks. This causes a lot of energy loss. However in many electric cars, rather than losing all the energy as heat, the tendency of the cars to continue in motion (even after we are no longer applying acceleration) allows the chance for us to hastily convert the motional energy into electricity using generators.