Forces Problems Worksheet

Forces Problems 1. What is the force of gravity at the Earths surface on: a. a 50 kg girl b. a 100 g bullet 2. If the gravitational field constant on the surface of the moon is 1.6 N/kg, what is the force of gravity acting on the two objects from 1) if they were on the moon? 3. Forces of 100 N [N] and 80 N [W] act simultaneously on an object, with mass of 10 kg. What is the object's acceleration? 4. Forces of 2.0 N and 1.0 N act on an object of mass 5.0 kg: a. Calculate the net force acting on the object. b. Calculate the acceleration of the object. 1.0 N 120 2.0 N 5. An empty railway flatcar of mass 15000 kg is being pulled along a smooth, horizontal track by a tractor travelling on a road parallel to the track. The rope joining the tractor and the flatcar makes and angle of 25° with the track. a. If the acceleration of the flatcar is 0.80 m/s², what is the force exerted by the rope on the flatcar. b. Why does the flatcar have no sideways acceleration if the rope exerts a sideways force? 6. A block of mass 2.0 kg is placed on a smooth plane, inclined to the horizontal at an angle of 15°. The force of gravity acting on the block is 20 N. a. What is the acceleration of the block down the plane? b. How far up the plane was the block released if if took 1.5 s to reach the bottom after it was released from rest? 7. A speedboat is pulling two water skiers using two ropes attached to the back of the boat. Each rope makes an angle of 30° on either side of the boats axis. The force exerted by each rope is 400 N. If the boat is moving in a straight line at a constant speed, what force must it be exerting to keep the pair of skiers moving? 8. A 3.0 kg toy is pulled by a force of 24 N. If the toy starts from rest, how far will it travel in the first 5.0 s? 9. A 40 kg sprinter starts from rest and 2.0 s later is running at a speed of 8.0 m/s. What is the average net horizontal force acting on the sprinter? What exerts this force? 10. An 8.0 g bullet travelling at 400 m/s passes through a heavy block of wood in 4.0 104 s, emerging with a velocity of 100 m/s. Ignore any motion of the wood: a. With what average force did the wood oppose the motion of the bullet? b. How thick is the block of wood? 11. A 0.22 calibre rifle shoots a bullet of mass 1.8 g with a muzzle velocity of 500 m/s. If the barrel is 25 cm long, what is the average force exerted on the bullet while it is in the barrel? 12. A motorist has a reaction time of 0.60 s (reaction time is the time between seeing a danger and applying the brakes). While driving at 72 km/h he sees a child run suddenly onto the road 40 m ahead. If the mass of the car is 1000 kg and the average horizontal force supplied by the brakes is 8000 N, will he stop in time? 13. A childs wagon experiences a frictional force of 73 N whenever it is in motion, regardless of the load it is carrying. A horizontal force of 128 N causes the wagon to accelerate at 5.0 m/s². The same applied force, with a child on the agon causes it to accelerate at 1.0 m/s². What is the mass of the child? 14. A sled of 6.0 kg mass is moving along a smooth horizontal ice surface with a velocity of vo. A force of 36 N is applied to the sled in the same direction as its motion, increasing its velocity to 2vo, while it moves 10 m. Find: a. the sleds original velocity b. the length of time the force was applied for. 15. A net force of 8.0 N gives a mass, ms, an acceleration of 2.0 m/s² and a mass, m2, an acceleration of 4.0 m/s². What acceleration would the force give the two masses if they were fastened together? 16. A gardener pushes down along a handle of a lawn mower of 20 kg mass with a force of 150 N. The handle makes an angle of 60º with the ground. Calculate the instantaneous acceleration of the mower if the frictional force between the mower and the ground at that instant is 25 N. 17. A man drags a package across the floor with a force of 40 N at some unknown angle. The mass of the package is 10 kg. If the acceleration of the package is 3.5 m/s² and friction is ignored, what angle does he pull the package at? Answers 1) 4.9 * 10 ^ 2 0.98 N 2) 80 N 0.16 N 3) 13 m/s² [N39W] 4) 1.7 N [E31N] 0.34 m/s² [E31N] 5) 1.3 * 10 ^ 4 N [25° to track] 6) 2.6 m/s² 2.9 m 7) 693 N 8) 1 * 10 ^ 2 * pi 9) 1.6 * 10 ^ 2 [forwards] 10) 6 * 10 ^ 3 N [backwards] 1 * 10 ^ - 1 m 11) 9 * 10 ^ 2 N [forwards] 12) yes (with 3.0 m to spare phew!!) 13) 44 kg 14) 6.3 m/s [forward] 1.1.s 15) 1.3 m/s² [forward] 16) 2.5 m/s² [forward] 17) 290