Eduqas GCSE Physics 4 Forces and Motion Exam Questions

About Eduqas GCSE Physics 4 Forces and Motion

Forces and motion is one of the most calculation-heavy topics in Eduqas GCSE Physics. It has three parts: speed, velocity and acceleration with motion graphs; forces, accelerations and Newton's laws of motion; and safety in public transport. You use the equations of uniform motion, interpret gradients and areas of distance-time and velocity-time graphs, apply F = ma, and use momentum and its conservation. The safety part covers reaction time, thinking and braking distances, large decelerations and car safety features. Examiners regularly set graph-reading questions, multi-step suvat style calculations and explanations of crumple zones and seat belts using momentum. SP4.2 measures the acceleration of a moving object.

What you need to know

• 4.1 Speed and velocity Speed = distance / time; velocity is speed in a given direction. Typical speeds: walking about 1.5 m/s, cycling about 6 m/s. On a distance-time graph the gradient is speed.
• 4.1 Acceleration and graphs Acceleration = change in velocity / time, in m/s2. On a velocity-time graph the gradient is acceleration and the area under the line is distance travelled. Equations given: v = u + at, x = 1/2(u + v)t, v^2 = u^2 + 2ax, x = ut + 1/2 at^2.
• 4.2 Newton's laws First law: an object stays at rest or at constant velocity unless a resultant force acts. Second law: F = ma. Third law: when two objects interact they exert equal and opposite forces on each other. Inertial mass measures how hard it is to change an object's velocity.
• 4.2 Momentum Momentum p = mv, in kg m/s. In a closed system total momentum before an event equals total momentum after. SP4.2: determine the acceleration of a moving object, for example a trolley with light gates.
• 4.3 Stopping distance Stopping distance = thinking distance + braking distance. Thinking distance increases with speed, tiredness, alcohol, drugs and distractions; braking distance increases with speed, worn tyres or brakes and wet or icy roads.
• 4.3 Safety features Large decelerations cause large forces. Seat belts, air bags and crumple zones increase the time taken to stop, reducing the rate of change of momentum and so the force on passengers.

Common mistakes in 4 Forces and Motion

• Treating speed and velocity as identical. Velocity includes direction, so an object moving in a circle at constant speed has changing velocity.
• Reading the area under a distance-time graph. Area under a velocity-time graph gives distance; the gradient of a distance-time graph gives speed.
• Applying Newton's third law to forces on the same object. Third law pairs act on two different objects and are the same type of force.
• Saying crumple zones reduce the change in momentum. The change in momentum is the same; it happens over a longer time, so the force is smaller.
• Forgetting to square the speed in v^2 = u^2 + 2ax, or using x for time. Write out the equation, substitute and rearrange carefully.

Try three 4 Forces and Motion exam-style questions