Worksheet Forces - PDF

## Forces Problems 1. What is the force of gravity at the Earths surface on: - a 50 kg girl - 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 1...

## Forces Problems 1. What is the force of gravity at the Earths surface on: - a 50 kg girl - 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: - Calculate the net force acting on the object. - Calculate the acceleration of the object. 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. - If the acceleration of the flatcar is 0.80 m/s², what is the force exerted by the rope on the flatcar. - 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 Ν. - What is the acceleration of the block down the plane? - 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 10-4 s, emerging with a velocity of 100 m/s. Ignore any motion of the wood: - With what average force did the wood oppose the motion of the bullet? - 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 wagon 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: - The sleds original velocity - The length of time the force was applied for. 15. A net force of 8.0 N gives a mass, m1, 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 60° 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 x10² N, 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 x10⁴ N [25° to track] 6. 2.6 m/s², 2.9 m 7. 693 N 8. 1.0 x10² m 9. 1.6 x10² N [forwards] 10. 6.0 x10³ N [backwards], 1.0 x10^-1 m 11. 9.0 x10² 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. 29°