Question

Dynamics is a branch of physics (specifically classical mechanics) concerned with the study of forces and torques and their effect on motion.Now answer the questions
(i)consider a car moving on a straight road with a speed of 100 m/s.The diatance at which the car is stoped (uk=0.5,g is 10)
(ii)A 60 kg body is pushed with just enough force to start it moving accross a floorand same force continues to act afterwards.the coefficient of static friction and sliding friction are 0.5 and 0.4 respectively.Acceleration is
(iii)A force of 50 N acts on a body of mass 12.5 kg which is at rest on a frictionless horizontal surface its displacement in 10 second is
plz answer all questions of para with detailed explanations

Answer 1

u = 100 m/sec  v = 0 
friction force = F = - μ_k m g = - 0.5 m g
acceleration due to friction = F / m = - 0.5 m g / m = -g/2  = - 5 m/sec/sec

s = (v^2 - u^2  ) / 2 a = 100^2 /2 * 5  =  1000 meters

2)
     m = 60 kg
       maximum value of Static friction = 0.5 * m g  = 0.5 * 60 * 10 = 300 Newtons
         force to start moving the mass = 300 newtons

    resultant force when 300 newtons pulls mass = 300 N - 0.4 * 60 * 10 = 60 N

       acceleration =  60 N / 60 kg = 1 m/sec^2

3)
         acceleration of the body  = F / m = 50 /12.5 = 4 m/sec^2
           s = u t + 1/2 a t^2 = 0 + 1/2 * 4 * 10^2 = 200 meters