Forces in Equilibrium

Question 1

What is a resultant force?

Answer 1

A resultant force is the overall force that acts on the object.

Question 2

Is force a vector or scalar?

Answer 2

Vector

Question 3

How is resultant force calculated?

Answer 3

If in the same direction they are added, if in opposing directions, they are subtracted. Always mention the direction of the resultant force

Question 4

Shortly after a ball is dropped, the air resistance is 5 N and the weight of the ball is 8 N.

Calculate the resultant force and say which direction it is acting.

Answer 4

3 N downwards

Question 5

What is a balanced force?

Answer 5

A balanced force is when the acting forces are both opposing and equal to each other. Meaning that the resultant force will be zero

Question 6

What is the state of an object if balanced forces are acting on it?

Answer 6

The object will either be stationary or travelling at constant velocity.

Question 7

A car is travelling down a motorway. The thrust(push) from the engine is 500 N and the air resistance acting against the car is also 500 N.
Describe the motion of the car.

Answer 7

The car is moving at constant velocity because the forces acting on it are balanced so there is no resultant force.

Question 8

A box is placed on a table. The weight of the force on the box acting downwards is 100 N. The table applies a 100 N normal reaction force on the box upwards.
Describe the movement of the box.

Answer 8

There is no resultant force acting on the object, so the box is at rest on the table.

Question 9

What is an unbalanced force?

Answer 9

Forces which act on an object and cause it to change direction or acceleration

Question 10

A rocket has just launched. The thrust from the engine is 50 000 N and the weight of the rocket is 10 000 N.
Describe the motion of the rocket.

Answer 10

40 000N upwards, The rocket is accelerating upwards.

Question 11

A sky diver has just opened her parachute. The weight of the sky diver is 500 N and the air resistance acting on her is 700 N

Answer 11

200 N upwards, the diver is decelerating.

Question 12

What happens if the resultant force of an object is zero?

Answer 12

The object will either remain stationary or at constant velocity. There will be no acceleration

Question 13

What is the relation ship acceleration and force?

Answer 13

Newton found that if mass is constant then acceleration is proportional to force.
a α F

Question 14

What is the relationship between acceleration and mass

Answer 14

if the force is constant then acceleration is inversely proportional to mass.
a α 1/m

Question 15

What is Force? And its equation?

Answer 15

A push and pull acting on an object as a result of interaction with another object. F = ma

Question 16

What is 1N?

Answer 16

1N is the force that causes a mass of 1kg to have an acceleration of 1ms^-2.
So 1N = k x 1kg x 1ms^-2

Question 17

What is the equation for Weight as a force?

Answer 17

W = mg

Question 18

How do you draw a free-body diagram?

Answer 18

Show the forces acting on an object in a free body diagram. The arrows represent the size and direction of the forces acting.

represent the object with a small box or dot
draw the arrows with a pencil and ruler
draw the arrows from the centre of the box or dot
label the arrow with the name of the force and the size of the force

Question 19

When is an object said to be in equilibrium?

Answer 19

When the two forces acting on it are equal and opposite, an object is said to be in equilibrium. The resultant is zero and the forces are balanced

Question 20

A child of weight 𝑊 on a swing is at rest due to the swing sear being pulled to the
side by a horizontal force 𝐹1
. The rope supporting the seat is then at an angle 𝜃
to the vertical, as shown in Figure 1.
a) Sketch a diagram and show the three forces acting on the object.
b) Calculate the balance forces

Question 21

An object of weight 𝑊 is supported by a vertical string, which is supported by two
strings at different angles 𝜃1 and 𝜃2 to the vertical, as shown in Figure 2. Suppose
the tension in the string at angle 𝜃1 to the vertical is 𝑇1 and the tension in the other
string is 𝑇2.
At the point 𝑃 where the strings meet, the forces 𝑇1, 𝑇2, and 𝑊are in equilibrium.
Calculate 𝑇1 and 𝑇2?

Question 22

A small object of weight 5.4 N is at rest on a rough slope at an angle of 30° to
the horizontal.

Question 23

What are the conditions for equilibrium of a body?

Answer 23

The resultant forces must be zero
The principle of moments must apply. (Since the moments balance out, the sum of moments is also equal to zero.)