Free-body diagrams and Newton's lawsEdexcel International A Level Physics: Subtopic test

1. 1
   A book of mass 1.5 kg rests on a horizontal table. The gravitational field strength is 9.81 N kg⁻¹.

   (a)

   The weight of the book is the gravitational force of the Earth on the book. Which force forms the Newton's third law pair with this weight?

   [1 mark]

   • Athe normal contact force of the table on the book
   • Bthe force of the book on the table
   • Cthe gravitational force of the book on the Earth
   • Dthe upward force of the table on the Earth

   (b)

   What is the weight of the book?

   [1 mark]

   • A14.7 N
   • B1.5 N
   • C0.15 N
   • D147 N

   (c)

   A student says that the weight of the book and the normal contact force of the table on the book are a Newton's third law pair because they are equal and opposite. Give two reasons why the student is wrong.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A van of mass 1500 kg travels along a straight, level road. The driving force from the engine is 3200 N and the total resistive force is 800 N.

   (a)

   What is the acceleration of the van?

   [1 mark]

   • A2.1 m s⁻²
   • B1.6 m s⁻²
   • C0.53 m s⁻²
   • D2.7 m s⁻²

   (b)

   At a higher speed the resistive force increases to 3200 N while the driving force stays at 3200 N. What happens to the motion of the van?

   [1 mark]

   • AIt continues to accelerate at 1.6 m s⁻²
   • BIt decelerates
   • CIt stops immediately
   • DIt continues at a constant velocity

   (c)

   The driver stops accelerating and the driving force becomes zero. The resistive force is still 800 N. Calculate the magnitude of the deceleration of the van.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A person of mass 70 kg stands on the floor of a lift. The gravitational field strength is 9.81 N kg⁻¹.

   (a)

   The lift accelerates upwards at 1.2 m s⁻². Calculate the force the floor exerts on the person.

   [3 marks]

   (b)

   The lift then accelerates downwards at 1.5 m s⁻². Calculate the force the floor exerts on the person and state whether the person would feel lighter or heavier than when the lift is stationary.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student uses a small steel ball, an electromagnet and an electronic timer connected to a trapdoor to determine the acceleration of free fall, g. The ball is held by the electromagnet at a measured height above the trapdoor. When the current is switched off the ball is released and the timer starts. The timer stops when the ball opens the trapdoor.

   (a)

   Describe how the student should use this apparatus to obtain a value for g, including how the results should be analysed.

   [6 marks]

   (b)

   The student obtains a value of g of 9.2 m s⁻² and suggests this is because the steel ball has a small mass, so its weight is small. Evaluate the student's suggestion.

   [6 marks]

   Total for question 4: 12 marks

End of questions