What is the magnitude of the third force?

Lots of points!!!!!!!!!!!!! newtons third law type stuff!?

• Lots of points!!!!!!!!!!!!! newtons third law type stuff!? HOW DO I DO THIS I NEED STEPS FOR EACH PROBLEM 2.) a car of mass m=1200 kg is traveling at a constant speed of 50-m/s. Suddenly the brakes are applied and the car is brought to a stop over a distance of 20m. Assuming constant break force find, the magnitude the breaking force and the time required to stop. 5.) a jet airplane accelerates on the runway at 3.0 m/s2. It has two engines which exert a total thrust of 3.0 x 10^5 N. What is the mass of this airplane. 6.) A horizontal force of 100N is required to push a crate across a factory floor at a constant speed. what is the net force acting on the crate?

• Answer:

  1.) vf^2 = v0^2 + 2ad vf = final velocity v0 = initial velocity a = acceleration d = distance 0^2 = 50^2 + 2a(20) -2500 = 40a a = -62.5 m/s^2 Breaking force: F = ma = 1200(62.5) = 75 000 N Time required to stop: d = v0t + 1/2at^2 20 = 50t + (1/2)(-62.5)t^2 31.25t^2 - 50t + 20 = 0 t = 0.8s 5.) F = ma 3.0 x 10^5 N = m(3) m = 1.0 * 10^5 kg 6.) 0N because constant speed means 0 acceleration. F = ma = m(0) = 0