Newton's third law and connected particlesEdexcel A-Level Maths: Flashcards

What these 12 flashcards ask

State Newton's third law.
Why do third-law pairs not cancel each other?
Are weight and normal reaction on a book at rest a third-law pair?
Resultant force on a particle in equilibrium?
Reaction on a person of mass m in a lift accelerating upwards at a?
Reaction on a person of mass m in a lift accelerating downwards at a?
What does an inextensible string tell you?
What does a light string over a smooth pulley tell you?
Acceleration of hanging masses m1<m2 over a smooth pulley?
How do you find the contact force between two blocks?
What happens to the tension when a hanging particle hits the floor?
Lift 250 kg and person 70 kg, a=1.5\ m s^{-2} upwards: cable tension?

Exam questions on Newton's third law and connected particles

A lift of mass 250 kg carries a person of mass 70 kg. The lift is raised by a vertical cable and accelerates upwards at $1.5\ \text{m s}^{-2}$ . Take $g=9.8\ \text{m s}^{-2}$ .
Find the tension in the cable.2 marks
Particle $A$ of mass 3 kg and particle $B$ of mass 5 kg are attached to the ends of a light inextensible string that passes over a smooth fixed pulley. The particles hang vertically and are released from rest with the string taut. Take $g=9.8\ \text{m s}^{-2}$ .
Particle $B$ is initially 1.5 m above the floor. Find the speed with which $B$ hits the floor.2 marks
Two blocks, $P$ of mass 4 kg and $Q$ of mass 6 kg, are in contact on a horizontal surface. A horizontal force of magnitude 30 N is applied to $P$ , directed towards $Q$ , and the blocks move together in a straight line.
The surface is smooth. Find the acceleration of the blocks and the magnitude of the contact force between them.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).