Newton's 1st Law

A car sets off from the traffic lights.

The forces are balanced.

• True

• False

Answer explanation

Car starts moving so is not stationary or moving with constant velocity. Newton's 1st law ⇒ forces are unbalanced.

A helicopter hovers over a field.

The forces are balanced.

• True

• False

Answer explanation

The helicopter remains stationary. Newton's 1st law ⇒ the forces are balanced.

A hot air balloon rises in the air at a constant velocity.

The forces are balanced.

• True

• False

Answer explanation

The balloon has a constant velocity. Newton's 1st law ⇒ the forces are balanced.

A bike flies through the air.

The forces are balanced.

• True

• False

Answer explanation

The bike is accelerating with the acceleration due to gravity so is not at rest or travelling at constant velocity. Newton's 1st law ⇒ the forces are not balanced.

A bird sits on a branch.

The forces are balanced.

• True

• False

Answer explanation

The bird is at rest. Newton's 1st law ⇒ forces are balanced.

A car travels along a road at a constant velocity of 20 ms-1. The force of friction that pushes the car forwards is 1000 N.

• 20,000 N

• 1000 N

• 50 N

• 0 N

Answer explanation

Velocity is constant so Newton's 1st law ⇒ Forces are balanced

A ball bounces off a wall.

The forces on the wall and ball are:

• balanced - unbalanced

• balanced - balanced

• unbalanced - balanced

• unbalanced - unbalanced

Answer explanation

The ball has a changing velocity but the wall is stationary.

A weight lifter lifts a 100 kg weight from the floor.

The force exerted by the weight lifter could be:

• 100 N

• 1000 N

• 1100 N

• 990 N

Answer explanation

To start the weight moving the force up must be bigger than the force down.

An elevator of mass 200 kg travels upwards at a constant velocity.

The tension in the cables is:

• 200 N

• 2000 N

• 1800 N

• 2200 N

Answer explanation

Velocity is constant so Newton's 1st law ⇒ forces are balanced. So upwards force from tension = weight = 2000N.