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 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum Aug 9th 2019, 07:32 AM #1 Junior Member   Join Date: Aug 2019 Posts: 1 Kinematics IB question, explanation needed Could someone please explain (c) and (d) in the question below and attachment. When I tried, I got 735 N, but that isn't the right answer. Thanks in advance for the help. 51 The diagram shows a person in an elevator pulling on a rope that goes over a pulley and is attached to the top of the elevator. The mass of the elevator is 30.0 kg and that of the person is 70 kg. a On a copy of the diagram, draw the forces on the person. b Draw the forces on the elevator. c The elevator accelerates upwards at 0.50 m s−2. Find the reaction force on the person from the elevator fl oor. d The force the person exerts on the elevator fl oor is 300 N. Find the acceleration of the elevator (g = 10 m s−2 ).   Aug 10th 2019, 02:26 PM #2 Junior Member   Join Date: Jan 2019 Posts: 25 forces on the person; Tension, T, upward Normal force of the elevator floor on the person, N, upward person weight, Mg, downward forces on the elevator; Tension, T, upward Normal force of the person on the elevator floor, N, downward elevator weight, mg, downward (c) a = 0.5 m/s^2 upward T + N - Mg = Ma T - N - mg = ma ---------------------- 2T -(M+m)g = (M+m)a 2T = (M+m)(g+a) = (100 kg)(10.5 m/s^2) = 1050 N T = 525 N using the net force equation on the person N = M(g+a) - T = (70 kg)(10.5 m/s^2) - 525 N = 210 N (d) N = 300 N T + N - Mg = Ma -(T - N - mg = ma) ----------------------- 2N - Mg + mg = Ma - ma 2N - (M-m)g = a(M-m) [2N - (M-m)g]/(M-m) = a [600 N - 400 N]/(40 kg) = 5 m/s^2 topsquark likes this.  Tags explanation, kinematics, needed, question Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post jackthehat Kinematics and Dynamics 3 Apr 22nd 2015 08:01 AM Anthonyk2015 Thermodynamics and Fluid Mechanics 1 Jan 25th 2015 12:49 PM Augine Periodic and Circular Motion 2 May 20th 2012 11:16 PM mephisto50 Kinematics and Dynamics 1 Jan 24th 2010 03:19 AM tsmith Kinematics and Dynamics 1 Sep 12th 2009 09:58 AM