SPH3U Practice Test A stationary box of mass 4.2 kg is given a push of 8.2 N [S] along a surface where the frictional force acting is 5.8 N [N]. The push lasts for 3.6 s and then the box is allowed to slide on its own until it comes to rest. (a) Draw free-body diagrams to show the box being pushed and sliding on its own. (b) Determine the acceleration of the box as it is being pushed. (c) Calculate the speed of the boxjust as the push ceases. (d) Determine the acceleration of the box as it is sliding on its own. Two crates. of mass 12.0 kg and 20.0 kg, respectively, are pushed across a smooth floor together, the 20 kg crate in front of the 12 kg crate. Their acceleration is 1.75 misl. Calculate each of the following. (a) the force applied to push the crates (b) the action-reaction forces between the two crates Recalculate (a) and (b) if the relative positions of the two crates are reversed. Three small children of mass 20.0 kg. 24.0 kg. and 16.0 kg. respectively. hold hands. as shown. and are pulled across a smooth frozen pond by a larger boy on skates, who pulls a horizontal rope being held by the first child. The skater pulls on the rope with a force of 135 N. Calculate each of the following. (a) the acceleration of the skater (b) the force with which each pair of children must hold hands. to ensure that the chain is not broken 24 kg (a) What is the net force required to give an automobile of mass lOO kg an acceleration of 4.5 m/sz? (b) What is the acceleration of a wagon of mass 20 kg if a horizontal force of 64 N is applied to it (ignore friction)? (c) What is the mass of a block of iron if a net force of 240 N causes it to accelerate across a smooth horizontal surface at 2.5 misl