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In this lesson, we will learn how to solve problems on Newton’s third law.

Q1:

An elevator is accelerating vertically upwards at 2 . 6 / m s 2 . A man of mass 1 2 4 k g is standing inside. Determine the reaction force of the floor on the man.

Q2:

A body of mass 75 kg was attached to a string fixed to the ceiling of an elevator. Starting from rest, the elevator began accelerating vertically upwards at 44 cm/s^{2}. During this time the tension in the string was 𝑇 1 . After accelerating, the elevator continued moving at the speed it had gained, at which point the tension in the string was 𝑇 2 . Finally, the elevator decelerated at 24 cm/s^{2}, at which point the tension in the string was 𝑇 3 . Determine the magnitudes of 𝑇 1 , 𝑇 2 , and 𝑇 3 . Consider the acceleration due to gravity to be 9.8 m/s^{2}.

Q3:

A body of mass 130 kg was placed on the floor of an elevator of mass 761 kg. The elevator ascended from rest and it covered 15 m while accelerating uniformly. Following this, it continued moving at the speed it had gained for a certain distance. Finally, it decelerated uniformly for 5 seconds over a distance of 10 m until its speed became 1 m/s. Find the force of the elevator’s motor 𝐹 when the elevator was accelerating upwards and the magnitude of the reaction 𝑅 exerted on the body by the floor of the elevator during the third stage of the motion. Take 𝑔 = 9 . 8 / m s 2 .

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