People A and B are taking a lift of mass 500 kg which has constant acceleration and the force from the rope that pulls it is 7500 N. The scales where the people stand show a reading of 720 N and 500 N.

Question 1 : Find the acceleration of the lift.Implementing Newton's Second Law we have : F net =Mα lift --->T-F A -F B -Mg =Mα lift ---> α lift =( T-F A -F B -Mg )/M (1)Substituting the relevant values of the forces given by the question we get that α lift = 2.75 m/s 2 ( where g= 9.81 m/s 2 )Question 2 : Find the masses of people A and B.Normally most students would equal the reading of the scale with the multiplication if the mass of the person with gravitational acceleration. This is not the case!! The person also has an upward acceleration equal to the lift's.Again by Newton's second Law we obtain : Person A F A - m A g = m A α lift ---> m A = F A /(g + α lift ) ----> m A = 57.3 kgPerson B F B - m B *g = m A lift ---> m B = F B /(g + α lift ) ----> m B =39.8 kgThis problem although not advanced or complicated can lead to misleading results if students have learned to work mechanically based on solved problems they have seen. As i stated in my description my goal is to avoid that and develop an analytical thinking of the students in order to spot tricky questions like this. Otherwise they would think their solution provided is correct.

Answered by Geri N. Physics tutor

1627 Views

See similar Physics A Level tutors

Related Physics A Level answers

All answers ▸

Why does a small puddle of water evaporate at room temperature, even though the temperature is way below the boiling point of water?


What is electromotive force (emf) and how can the emf of a battery be measured?


A ball with radius 10cm is filled with an ideal gas at pressure 2*(10)^5Pa and temperature 300K. The volume of the gas is changed at constant pressure so that the radius of the ball is reduced with 1cm. Find the amount of gas and the new temperature


A spacecraft called Deep Space 1, mass 486 kg, uses an “ion-drive” engine which expels 0.13 kg of xenon propellant each day at 30kms^-1. What is the initial increase in speed of the spacecraft


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences