Forces in two dimensions | Starter Quiz | Oak National Academy

How many newtons (N) are there in 53 kN?

• 5300 N

• 53 000 N

• 530 000 N

• 53 000 000 N

Answer explanation

kN stands for kilonewton, and there are a thousand newtons in a kilonewton, so 53 kN = 53 thousand N, or 53 000 N.

The diagram shows a force arrow drawn on a grid of 1 cm squares. What is the magnitude of the force?

• left

• right

• 3 N

• 6 N

• 12 N

Answer explanation

The magnitude of a force is its size and is represented by the length of the arrow. 1 cm represents 2 N and the arrow is 6 cm long, so the force is 6 × 2 = 12 N.

There is a law of physics which states that an object will remain at rest, or in motion in a straight line at constant speed, unless a resultant force is acting on it. What is the name of this law?

• Newton’s First Law of motion

• Newton’s Second Law of motion

• Newton’s Third Law of motion

• Newton’s Fourth Law of motion

Answer explanation

Isaac Newton wrote three laws of motion, and this is the first. (The third law is about pairs of equal and opposite forces.)

What is the magnitude of the resultant force in the diagram shown?

• 203 N

• 248 N

• 253 N

• 293 N

Answer explanation

The sum of forces to the left is 20 + 25 = 45 N. The force to the right is 248 N. The resultant force is the difference: 248 – 45 = 203 N (to the right).

The diagram shows an object with a single force acting on it. Which of the following are possible descriptions of the object’s motion?

• The object is moving to the left at constant speed.

• The object is moving to the right at constant speed.

• The object is accelerating.

• The object is decelerating.

Answer explanation

There is a resultant force of 5 N to the left, so the object’s velocity must be changing and it cannot be moving in a straight line at constant speed. If it is moving to the left then it is accelerating and if it is moving right it is decelerating.

A child throws a ball straight up. Which of the following is a correct free body diagram of the ball as it travels upwards?

• 
• 
• 
• 

Answer explanation

Weight is the gravitational pull of the Earth and always acts downwards. Air resistance acts in the opposite direction to the motion, so it acts downwards. (The resultant force is downwards so the ball decelerates as it travels up.)