GCSE Physics Forces and Motion — Questions and Answers
Question 1: Which of the following is a vector quantity?
- Speed
- Distance
- Mass
- Velocity (Correct answer)
Correct answer: Velocity
Velocity has both magnitude and direction, so it is a vector.
Scalar quantities have magnitude only, for example speed, distance, mass, time and energy. Vector quantities have both magnitude and direction, for example velocity, displacement, force, acceleration and momentum. Velocity is speed in a stated direction, which is why it is a vector.
Question 2: A car travels 150 m in 6 s. What is its average speed?
- 900 m/s
- 25 m/s (Correct answer)
- 0.04 m/s
- 156 m/s
Correct answer: 25 m/s
Speed = distance ÷ time = 150 ÷ 6 = 25 m/s.
Average speed is calculated using speed = distance ÷ time. Substituting the values gives 150 m ÷ 6 s = 25 m/s. Always check that the units are consistent (metres and seconds give metres per second) and show your working in the exam.
Question 3: A resultant force of 20 N acts on a mass of 4 kg. What is the acceleration?
- 80 m/s²
- 0.2 m/s²
- 5 m/s² (Correct answer)
- 24 m/s²
Correct answer: 5 m/s²
F = ma, so a = F ÷ m = 20 ÷ 4 = 5 m/s².
Newton's second law states that resultant force = mass × acceleration (F = ma). Rearranging gives a = F ÷ m. Substituting 20 N ÷ 4 kg gives 5 m/s². The direction of the acceleration is the same as the direction of the resultant force.
Question 4: What does the gradient of a distance-time graph represent?
- Speed (Correct answer)
- Acceleration
- Distance travelled
- Force
Correct answer: Speed
The gradient of a distance-time graph gives the speed.
On a distance-time graph, the gradient (slope) equals distance ÷ time, which is speed. A straight sloping line shows constant speed, a horizontal line shows the object is stationary, and a curve shows changing speed (acceleration or deceleration). Do not confuse this with a velocity-time graph, where the gradient gives acceleration and the area gives distance.
Question 5: What is the weight of a 5 kg object on Earth? (gravitational field strength = 9.8 N/kg)
- 5 N
- 0.51 N
- 14.8 N
- 49 N (Correct answer)
Correct answer: 49 N
Weight = mass × gravitational field strength = 5 × 9.8 = 49 N.
Weight is the force acting on an object due to gravity and is calculated using weight = mass × gravitational field strength (W = mg). On Earth g is approximately 9.8 N/kg, so 5 kg × 9.8 N/kg = 49 N. Weight is measured in newtons, whereas mass is measured in kilograms and stays the same wherever the object is.
Question 6: Two forces act on an object in opposite directions: 30 N to the left and 12 N to the right. What is the resultant force?
- 42 N to the left
- 18 N to the left (Correct answer)
- 18 N to the right
- 42 N to the right
Correct answer: 18 N to the left
Opposite forces are subtracted: 30 − 12 = 18 N, in the direction of the larger force (left).
The resultant force is the single force that has the same effect as all the forces acting together. When two forces act along the same line in opposite directions, you subtract them: 30 N − 12 N = 18 N. The resultant acts in the direction of the larger force, so the answer is 18 N to the left.
GCSE Physics Forces and Motion
Which of the following is a vector quantity?