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physics Physics For High Schools (KS4)
 
Solved problems for the chapter:
 

Resultant Force

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Detailed solution steps are available at:
 
https://en.openprof.com/wb/chapter:resultant_force/5058/


Example 1.

Determine whether or not, each of the following statements is correct:


  • An apple is hanging on a branch of a tree. The resultant of the forces acting on the apple is equal to the weight of the apple.


  • A car is standing in front of a traffic light. The sum of all the forces acting on the car is zero.


  • A car moves evenly on a level road. The resultant of all the forces acting on the car is equal to the force of the engine.


  • We hang a 4 N weight on a spring balance which is attached to a retort stand. It stretches by 2 cm. In the end, the resultant of the forces acting on the weight is zero.


  • There is a package on a table. Because it is at rest, no force acts on it.


    
Example 2.

A metal ball weighing 2 kg falls to the ground.

  • What force acts on the ball?

  • Determine the magnitude, direction, and line of action of this force.

  • Draw the force to scale.

    
3.

A table weighing 200 N has a triangular base as shown in the figure.

  • What is the magnitude and direction of the force with which the table acts on the ground?

  • Where is the line of action of this force?

  • Draw the force to scale.


    
4.

A student has a schoolbag in his hand as shown in the picture. The weight of the schoolbag is 20 N. Determine the size, direction, and centre of gravity of the forces acting on the schoolbag and draw them to scale.


    
5.

A boat, tied to a rope, is towed on the water at a speed of 2 m/s. The traction force is 600 N. With what force does the boat resist the flow of the water?


    
6.

A ball rolls uniformly and in a straight line on a flat surface at a speed of 2 m/s - Figure A. At some point, two equal but oppositely directed forces of magnitude 3 N each begin to act on the ball - Figure B. How will the ball move after the forces start to act?


    
7.

A skier of weight 600 N steps on soft snow. The moment he steps on the snow, the force of the ground is 400 N.

  • What is the resultant force and in which direction does it act?

  • What force needs to change and by how much for the skier to rest?


    
8.

Given two forces and . Graphically and computationally determine the resultant of these two forces if they are:

  • parallel and in the same direction,

  • parallel and in opposite direction.

    

9.

Two opposing forces act on a crate, as shown in the figure. The first force is 18 N while the second force is 12 N.

  • On what scale are they drawn?

  • Graphically and computationally determine their resultant force.


    
10.

Jack pulls a cart with a force of 15 N. Tim helps him by pushing the cart with a force of 10 N from behind. Graphically and computationally determine the resultant of the forces on the cart.

    
11.

Seven friends compete in a tug of war. A group of four friends pulls the rope to the right while the other three pull to the left - see picture. The right group pulls with forces of 20 N, 80 N, 40 N, and 60 N, and the left with forces of 60 N, 80 N, and 80 N. Which group acts with greater force on the rope and by how much?


Pulling a rope. The forces are not drawn to scale!

    
12.

The resultant of all forces acting on a box must be greater than 300 N for the box to move. Forces of 600 N to the right and 800 N to the left act on the box, as shown in the figure. Will the box move?


The forces on the box are not drawn to scale .

    
13.

A table weighing 200 N stands on four legs. How much force does each foot exert on the ground?


    
14.

Two forces, and are arranged as shown in the diagram.

  • What is the scale of the forces?

  • Graphically and computationally find the resultant of the forces.


    
15.

Mabel and Jack pull a rope in the same direction, each with a force of , and Bennett pulls the same rope in the opposite direction, with a force of .


  • Determine the resultant force computationally.

  • Determine the resultant of the forces graphically.

  • Does the resultant force point in the direction of Bennett or Mabel and Jack. Justify your answer.

    
16.

John wants to use a fixed pulley to lift a load weighing 800 N. His mass is 60 kg. Will he succeed?


    
17.

A pair of parallel forces are arranged as shown in the diagram. The selected scale used is . Find, by drawing and computing, the resultant force.


    
18.

A pair of parallel forces, and are arranged as shown in the diagram. Find the scale and hence calculate, by drawing and calculation, the resultant force.


Parallel forces .

    

19.

Ted pushes a table to the right with a force of , and Blake pushes the table with a force of in the opposite direction.


  • Determine the scale of the forces if Blake's force is long.

  • By drawing, determine how much force Ted would have to push to make the resultant equal to zero.

  • In which direction should Ted be pushing? Clarify the answer.

    
20.

Nick and Sam each hold two attached springs on their sides and pull them as shown in the picture. Nick acts on the left spring balance with a force of 8 N. How much force do the left and right spring balances show? What do they show if Sam reduces the force to 6 N?


    
21.

A spring balance attached to a stand has a weight of 0.5 N hung on it. Another similar spring balance, attached below the weight, also has another 0.5 N weight hung on it - see the figure below. Each spring balance weighs 0.3 N. How much force do both spring scales show?