Chapter 10 - Forces and Motion

Question 1

Force diagrams: A block of weight W is being pulled to the right by a force, P, across a rough horizontal plane. Draw a force diagram to show all the forces acting on the block

Answer 1

Question 2

When is an objects said to be in equilibrium?

Answer 2

When the forces acting upon that object are balanced

Question 3

Newton’s first law:

Answer 3

Newton’s first law of motion states that an object at rest will stay at rest, and that an object moving with constant velocity will continue to move with constant velocity unless an unbalanced force acts on the object

Question 4

Resultant forces:

Answer 4

When there is more than one force acting on an object you can resolve the forces in a certain direction to find the resultant force in that direction. The direction you are resolving in becomes the positive direction. You add forces acting in this direction and subtract forces acting in the opposite direction

Question 5

Resultant force notation:

Answer 5

Question 6

A resultant force acting on an object will cause the object to…

Answer 6

accelerate in the same direction as the resultant force

Question 7

Answer 7

Question 8

Forces as vectors:

Answer 8

You can write forces as vectors using i-j notation or as column vectors

Question 9

How to find the resultant force using forces as vectors:

Answer 9

You can find the resultant of two or more forces given as vectors by adding the vectors

Question 10

When a particle is in equilibrium, the resultant vector force will be…

Answer 10

0i + 0j

Question 11

Newton’s second law:

Answer 11

Newton’s second law of motion states that the force needed to accelerate a particle is equal to the product of the mass of the particle and the acceleration produced:
- F = ma

Question 12

Weight =

Answer 12

• Weight = mass x gravitational constant
• W = mg

Question 13

Connected particles:

Answer 13

If a system involves the motion of more than one particle, the particles may be considered separately.
However, if all parts of the system are moving in the same straight line, then you can also treat the whole system as a single particle

Question 14

To find the tension in a string…

Answer 14

particles need to be considered separately. The answer should be the same for both particles = tension in the string is always the same (unless the system changes from having 2 particles to 1)

Question 15

Newton’s third law:

Answer 15

Newton’s third law states that for every action there is an equal and opposite reaction

Question 16

Pulleys:

Answer 16

• The problems answered will assume that the particles are connected by a light, inextensible string, which passes over a smooth pulley. This means that the tension in the string will be the same on both sides of the pulley. The parts of the string each side of the pulley will be either horizontal or vertical
• The system involving a pulley cannot be treated as a single particle. This is because the particles are moving in different directions

Question 17

When solving pulley questions…

Answer 17

make the whole thing one line, so that T cancels out, and so you can solve F = ma

Question 18

Reaction force:

Answer 18

When a particle is accelerating, the reaction force is not equal to the weight of the particle and must always be calculated