Forces in action
Start with the object and draw all forces acting on it. Their vector sum determines acceleration; zero resultant force gives constant velocity, including rest.
Specification outcomes (20)
- 3.2.1(a) Apply Newton’s second law, F = ma.
- 3.2.1(b) Define the newton as the unit of force.
- 3.2.1(c) Understand weight of an object, W = mg.
- 3.2.1(d) Define and identify tension, normal contact force, upthrust and friction.
- 3.2.1(e) Draw and interpret free-body diagrams.
- 3.2.1(f) Describe one- and two-dimensional motion under constant force.
- 3.2.2(a) Define drag as the frictional force experienced by an object travelling through a fluid.
- 3.2.2(b) Explain factors affecting drag for an object travelling through air.
- 3.2.2(c) Describe motion of objects falling in a uniform gravitational field in the presence of drag.
- 3.2.2(d)(i) Define and describe terminal velocity.
- 3.2.2(d)(ii) Use techniques and procedures to determine terminal velocity in fluids, such as a ball bearing in a viscous liquid or cones in air.
- 3.2.3(a) Define moment of a force; moment = F × x.
- 3.2.3(b) Define couple and torque of a couple; torque = F × d.
- 3.2.3(c) State and apply the principle of moments.
- 3.2.3(d) Define and determine the centre of mass and centre of gravity experimentally.
- 3.2.3(e) Describe equilibrium of an object under the action of forces and torques.
- 3.2.3(f) Apply the condition for equilibrium of three coplanar forces using the triangle of forces.
- 3.2.4(a) Define density; ρ = m / V.
- 3.2.4(b) Define pressure; p = F / A for solids, liquids and gases.
- 3.2.4(c) Use p = hρg to calculate pressure in fluids; understand upthrust and Archimedes’ principle.
H156 v2.0 · May 2026
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PhysicsUK practice
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An athlete and racing wheelchair have a combined mass of $84.0\,\mathrm{kg}$. At the start of a straight training run, the wheelchair is already moving at $2.00\,\mathrm{m\,s^{-1}}$. For the next $1.50\,\mathrm{s}$, the athlete produces a constant forward driving force of $420\,\mathrm{N}$. A constant rolling resistance of $84.0\,\mathrm{N}$ acts backward. After this $1.50\,\mathrm{s}$ push, the athlete stops producing a driving force. Assume the rolling resistance remains $84.0\,\mathrm{N}$ until the wheelchair stops. (a) Calculate the resultant force and acceleration during the push. [3] (b) Calculate: (i) the speed at the end of the push; (ii) the distance travelled during the push. [4] (c) Calculate the acceleration after the driving force is removed. [2] (d) Calculate: (i) the time taken to stop after the push; (ii) the distance travelled after the push. [3] (e) Calculate the total distance travelled from the start of the stated motion until the wheelchair stops. [1]
Matched by specification tags · 13 marks
Try this question now →A technician calibrates the spring bumper of a small instrument trolley. Figure 1 shows the force F needed to compress the spring by x from its natural length. The graph is a straight line through (0, 0), (0.020 m, 1.2 N), (0.040 m, 2.4 N) and (0.060 m, 3.6 N). The trolley has mass 0.60 kg. It is released from rest against the spring at compression 0.060 m on a horizontal track. A constant resistive force of 0.60 N opposes the motion as soon as the trolley moves. The spring's mass is negligible and its deformation is elastic. The trolley loses contact with the spring at its natural length. There are no other energy losses. (a) Use the gradient of the force-compression graph to determine the spring constant. [2] (b) Use the graph to calculate the work needed to compress the spring from its natural length to 0.060 m. [2] (c) Calculate the acceleration just after release, stating its direction relative to the bumper. [3] (d) Calculate the speed when the trolley loses contact with the spring. Account for the work done against resistance. [3] (e) Explain why a single constant-acceleration equation cannot describe the whole interval while the trolley is in contact with the spring. [2] (f) Calculate the distance travelled after losing contact before the trolley stops. Use a constant-acceleration equation for this part. [3]
Matched by specification tags · 15 marks
Try this question now →A sensor is suspended from a small ring by a light vertical cord. The ring is held by an inclined spring on its left and a light horizontal cord on its right, as shown in Figure 2. The spring slopes upwards to the left at 40.0° above the horizontal. The sensor's weight is 12.0 N. The ring and cords have negligible mass. All forces act in one plane through the centre of the ring, which is at rest. The spring constant is 80.0 N m⁻¹ and the spring obeys Hooke's law for extensions up to 0.300 m. (a) Use vertical equilibrium to calculate the tension in the inclined spring. [3] (b) Calculate the tension in the horizontal cord. [2] (c) Calculate the spring's extension and check whether using Hooke's law is consistent with the stated proportional range. [3] (d) A pupil claims that the spring tension is 12.0 N because the sensor is at rest. Explain why this claim is incorrect. [2]
Matched by specification tags · 10 marks
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