IGCSE · 1 · structured
Motion, forces and energy · Question 7
Motion, forces and energy · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 9
- Topics
- 2
- Answer
- Complete
A car of mass 1200 kg starts from rest on a straight, level road. It reaches a speed of 24 m/s in 8.0 s. The forward force produced by the engine during this time is 4500 N.
- (a)
State State the equation linking acceleration, change in velocity and time taken.
1 mark - (b)
Calculate Calculate the acceleration of the car.
2 marks - (c)
Calculate Calculate the resultant force acting on the car.
2 marks - (d)
Determine Determine the total resistive force acting on the car during this time.
2 marks - (e)
Explain The car later travels along the same road at a constant speed of 30 m/s. Explain, in terms of the forces acting, why the speed is constant.
2 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
State State the equation linking acceleration, change in velocity and time taken.
Answer the command word directly and use precise physical vocabulary. Include only the distinct features or facts that earn marks, without burying them in unrelated background information.
- 1
a = Δv / Δt, in words or symbols, with symbols defined or standard
(b)
Calculate Calculate the acceleration of the car.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
a = 24 / 8.0
- 2
a = 3.0 m/s² (unit required)
(c)
Calculate Calculate the resultant force acting on the car.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
F = ma = 1200 × 3.0
- 2
F = 3600 N (unit required)
(d)
Determine Determine the total resistive force acting on the car during this time.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
recognises resistive force = forward force − resultant force
- 2
4500 − 3600 = 900 N
(e)
Explain The car later travels along the same road at a constant speed of 30 m/s. Explain, in terms of the forces acting, why the speed is constant.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
the resultant force on the car is zero
- 2
because the forward force from the engine is equal in size to the total resistive force (and opposite in direction)
Private on this device