Forces and their interactions

Show — 3 marks

A delivery driver pushes a cardboard box across a wooden warehouse floor. The box has a mass of 25 kg and experiences a friction force of 80 N opposing its motion. The driver applies a horizontal pushing force to move the box at constant velocity.

(a) Show that the pushing force applied by the driver is 80 N. [1 mark]
(b) The driver then pushes with a force of 120 N. Show that the resultant force on the box is 40 N in the direction of motion. [1 mark]
(c) Using F = ma, show that the acceleration of the box is 1.6 m/s². (You may assume the friction force remains constant.) [1 mark]

Show mark scheme

(a) At constant velocity, acceleration is zero, so resultant force = 0 N (or pushing force equals friction force) / pushing force = 80 N
(b) Resultant force = 120 N − 80 N = 40 N (or equivalent correct subtraction of friction from applied force)
(c) a = F ÷ m = 40 ÷ 25 = 1.6 m/s² (or equivalent correct rearrangement and calculation)

Explain — 3 marks

An astronaut with a mass of 80 kg stands on the surface of the Moon, where the gravitational field strength is approximately 1.6 N/kg. On Earth, the gravitational field strength is 10 N/kg. The astronaut's friend remains on Earth with the same mass of 80 kg.

(a) Explain why the astronaut's weight on the Moon is different from their weight on Earth, even though their mass remains the same. [2 marks]
(b) Explain why the astronaut and Earth exert gravitational forces on each other, using the concept of gravitational field interaction. [1 mark]

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(a) Weight is the force of gravity acting on an object (or gravitational force/interaction between object and planet)
(a) Weight depends on gravitational field strength, which is different on the Moon compared to Earth (Moon has weaker gravitational field strength)
(b) The Moon creates a gravitational field around it; the astronaut is in this field and experiences a force. The astronaut also creates a gravitational field that acts on the Moon (or: gravitational forces are interactions between two objects with mass, where each object exerts a force on the other)

Show — 2 marks

A student is using a force meter to investigate the weight of different objects on Earth. They measure the weight of a 2 kg mass using a calibrated spring balance. The gravitational field strength on Earth is 10 N/kg.

(a) Show that the weight of the 2 kg mass is 20 N. [1 mark]
(b) Explain why the weight of this mass would be different on the Moon, where the gravitational field strength is approximately 1.6 N/kg. [1 mark]

Show mark scheme

(a) Correct use of weight = mass × gravitational field strength (W = m × g), showing 2 × 10 = 20 N
(b) Recognises that weight depends on gravitational field strength / the Moon has a weaker gravitational field than Earth, so the weight would be less

Describe — 2 marks

A student holds a book in their hand. The book has a mass of 0.5 kg and remains stationary in the air. The gravitational field strength on Earth is 10 N/kg.

(a) Describe the interaction between the Earth and the book that produces the weight of the book. [1 mark]
(b) Describe how the student's hand exerts a force on the book to keep it stationary. [1 mark]

Show mark scheme

(a) The Earth pulls/attracts the book downwards due to gravity (or equivalent statement showing gravitational attraction between two objects)
(b) The hand pushes/exerts an upward force on the book (or equivalent statement describing contact force acting upward to balance weight)

Show — 3 marks

Explain — 3 marks

Show — 2 marks

Describe — 2 marks

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