Question

Some problems adapted from . O Bird, Science for Engineering -K Johnson, Advanced Physics -. S Walker, Physics O. Problem 1 The momentum of a body is 160kgms when it has a velocity of 2.5ms. Determine the mass of the body Problem 2 Calculate the momentum of a car which has a mass of 750kg when it moves with a constant velocity of 108kmhr Problem 3 A football of mass 200g has a momentum of 5kgms. What is the velocity of the ball in kmhr'? Problem4 A wagon of mass 8 tonne is moving with a velocity of 5ms when it collides with another wagon of mass 12 tonne which is stationary. After the collision the wagons are locked together, determine the common velocity of the wagons after impact. Problem 5 A ball of mass 40g is moving with a velocity of 5ms when it strikes a stationary ball of 30g. The velocity of the 40g ball after impact is 4ms in the same direction as before impact. Determine the velocity of the 30g ball after impact. Problem 6 A car of mass 800kg was stationary when hit head-on by a lorry of mass 2000kg travelling at 15ms. Assume no brakes are applied and the car and lorry move as one, determine the velocity of the wreckage immediately after impact. Problem7 During a serve, a tennis racket is in contact with the ball for 25ms. The ball has a mass of 60g and leaves the racket with a horizontal velocity of 31ms1. If the initial horizontal velocity is zero, determine: a) The change in momentum of the ball b) The impulse from the racket o) The average force exerted on the ball by the racket.

Answer 1

Given momentum = p = 160 kg m/s velocity = v = 2.5 m/s To determine mass = m P = Momentum = mv implies 160 = m times 2.5 - from given data implies m = 64 kg Given: mass = 750kg, velocity = 108 km/hr Momentum = 750 times 108 = 81,000 kg km/hr In S I unit Momentum = 81000 times 5/18 = 22,500 kg m/s Given: mass = m = 200g = 0.2 kg Momentum = P = 5kg m/s To find: velocity = v (in km/hr) Using Momentum = P = mv, we have 5 - 0.2 times v implies v = 25 m/s To convert to km/hr divide by 1000(m rightarrow km) and multiply by 3600(s rightarrow hr) implies v = 25/1000 times 3600 = 90 km/hr Given Mass of wagon - 1 = 8000 kg = m_1 velocity of wagon - 1 = 5 m/s = m_2 Mass of wagon - 2 = 12000 kg = v_1 Velocity of wagon - 2 = 0 = v_2