Chapter 4: Dynamics

The resultant force acting on an object of mass 10 kg is 25 N.

What is the acceleration of the object?

• 0.40 m/s²

• 2.5 m/s²

• 4.0 m/s²

• 25 m/s²

Answer explanation

Use the formula F = ma.

25 = 10 x a

a = 25 / 10

a = 2.5 m/s2

A car with a mass of 1500 kg is subjected to a net force of 3000 N.

What is the acceleration of the car?

• 0.50 m/s²

• 2.0 m/s²

• 5.0 m/s²

• 20 m/s²

Answer explanation

Use the formula F = ma.

3000 = 1500 x a

a = 3000 / 1500

a = 2.0 m/s2

An object with a mass of 5 kg experiences a net force of 15 N.

What is the acceleration of the object?

• 0.33 m/s²

• 3.0 m/s²

• 3.3 m/s²

• 30 m/s²

Answer explanation

Use the formula F = ma.

15 = 5 x a

a = 15 / 5

a = 3.0 m/s2

A truck with a mass of 6000 kg is acted upon by a net force of 3000 N.

What is the acceleration of the truck?

• 0.50 m/s²

• 1.0 m/s²

• 2.0 m/s²

• 5.0 m/s²

Answer explanation

Use the formula F = ma.

3000 = 6000 x a

a = 3000 / 6000

a = 0.50 m/s2

A block of weight W is at rest on a table.

Force F and force W are an action-reaction pair of forces.

Which describes force F?

• the downward normal force that the table exerts on the block

• the force that the block exerts on the Earth towards the block

• the gravitational force that the Earth exerts on the table

• the upward contact force that the table exerts on the block

Answer explanation

Action-reaction pairs are forces which are..

1. 1. Equal

2. 2. Opposite in direction

3. 3. Acts on different bodies.

Example - Holding an apple

1. 1. Force on apple by hand

2. 2. Force on hand by apple

So W is weight which is gravitational force of Earth on table. The other force should act on Earth (different bodies).

The table should not be even considered.

What's the resultant force?

• 0.0 N

• 10 N

• 20 N

• 100 N

Answer explanation

Resultant force is the result of adding all the forces on the object.

Left 10N and right 10N will cancel each other out.

Answer: 0.0 N

What's the resultant force?

• 5.0 N

• 25 N

• 35 N

• 140 N

Answer explanation

Resultant force is the result of adding all the forces on the object.

mass is not required when you can just add up the forces.

20 - 15 = 5.0 N

Answer: 5.0 N

The resultant force acting on the box is 20 N to the left.

What could F be?

• 4.0 N

• 10 N

• 14 N

• 30 N

Answer explanation

Resultant force is the result of adding all the forces on the object.

Mass is not required when you can just add up the forces.

F - 10 = 20

F = 30

Answer: 30 N

The resultant force acting on the box is 20 N to the right.

What could F be?

• 15 N

• 35 N

• 175 N

• 200 N

Answer explanation

Resultant force is the result of adding all the forces on the object.

Mass is not required when you can just add up the forces. Take note of the direction of the forces.

F + 5 - 20 = 20

F = 35

Answer: 35 N

The box is moving with a constant speed.

What could F be?

• 1.4 N

• 7.0 N

• 35 N

• 42 N

Answer explanation

It's moving at constant speed means there is no acceleration and forces are balanced on the object.

So F = 7.0 N