AQA GCSE Physics (8463), Higher tier · Forces › Forces and their interactions
Practise Resultant forces. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Name the two other forces acting on the balloon as it rises.
Weight and air resistance.
The tension in the cable is increased to 3900 N. Calculate the resultant force on the crate and give its direction.
300 N upwards N
State what it means for an object when the resultant force acting on it is zero.
It stays at rest or moves at constant velocity (it is in equilibrium).
What word describes an object when the resultant force acting on it is zero?
Equilibrium.
A tractor pulls a trailer using a chain, which exerts a forward force of 2400 N on the trailer. Resistive forces (friction and air resistance) on the trailer total 2400 N. The trailer is already moving forward. Calculate the resultant force on the trailer.
0 N
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) Which of these is the correct definition of the resultant force on an object? Tick (✓) one box.[1]
The largest of the forces acting on the object
The single force that has the same effect as all the forces acting on the object together
The force needed to keep the object still
The force that always acts against the object’s motion
(b) State what it means for an object when the resultant force acting on it is zero.[1]
(c) A stationary crate is pushed with a force of 90 N to the right. Friction of 90 N acts to the left. Calculate the resultant force on the crate.[2]
Show the answer and mark scheme
(a)Answer: The single force that has the same effect as all the forces acting on the object together
(b)Answer: It stays at rest or moves at constant velocity (it is in equilibrium).
the object stays at rest, or continues to move at a constant velocity (it is in equilibrium)
(c)Answer: 0 N
90 − 90
0 (N)
Question 2Medium6 marks
A crane lifts a crate using a vertical steel cable. The weight of the crate is 3600 N. Ignore air resistance.
(a) The crate hangs at rest just above the ground. What is the tension in the cable?[1]
(b) The tension in the cable is increased to 3900 N. Calculate the resultant force on the crate and give its direction.[2]
(c) Describe the motion of the crate while the tension is 3900 N.[1]
(d) Later, the crate moves upwards at a constant speed. Give the tension in the cable. Explain your answer.[2]
Show the answer and mark scheme
(a)Answer: 3600 N
3600 (N)
(b)Answer: 300 N upwards N
300 (N)
upwards
(c)Answer: It accelerates upwards.
accelerates upwards / speeds up (moving upwards)
(d)Answer: 3600 N, because the resultant force is zero at constant speed.
3600 (N)
(constant speed so) the resultant force is zero / the forces are balanced, so the tension equals the weight
Question 3Hard6 marks
A crane lifts a heavy load at a constant speed, using a vertical cable.
Using ideas about resultant force and equilibrium, explain how the crane can lift the load at a constant speed. Then explain what would happen to the load’s motion immediately if the tension in the cable suddenly increased, or if it suddenly decreased.[6]
Show the answer and mark scheme
at a constant speed the load is in equilibrium, so the resultant force on it is zero
this means the tension in the cable must be equal in size to the weight of the load, and act in the opposite direction
if the tension suddenly increases above the weight, there is a resultant force upwards, so the load accelerates upwards (speeds up while moving up)
if the tension suddenly decreases below the weight, there is a resultant force downwards, so the load decelerates while moving up (or accelerates downwards)
the direction of the load’s acceleration is always the same as the direction of the resultant force
at the very start of the lift, from rest, the tension must be greater than the weight, so that the load accelerates upwards from rest in the first place
Marked with levels of response: the full level descriptors are in the app.