Friction, Newton’s second law and power on a horizontal road
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 1 worked example, 6 practice questions, 1 real past-paper question with the answer explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why the winch has to work
- Friction
- Newton’s second law
Read the transcript of the teaching part
Last time
Before we start: last time, in A vehicle towing a trailer, vertical motion against a resistance, and a lift, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why the winch has to work
Drag a heavy block along the ground and you feel it resist. That resistance is friction. The winch that pulls it must deliver power, and power equals force times speed. Put friction and power together and you can find the speed.
Friction
Friction opposes the motion, or the tendency to move. It acts along the surface. The maximum value is mu times the normal reaction R. This is limiting friction, F equals mu R. On a horizontal surface with no other vertical forces, R equals the weight, m g.
Newton’s second law
The resultant force equals mass times acceleration. Resolve along the direction of motion. At constant speed the acceleration is zero, so the driving force equals the resistance. If the object is on the point of moving, friction is limiting, F equals mu R.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Power on a horizontal road · Power on an inclined road.
The whole chapter: Energy, Work and Power.
Chapter 4.5: Energy, work and power
- Friction, Newton’s second law and power on a horizontal road 6 min
- Work, energy and power: average power, slopes and variable resistance 6 min
- Work and energy on curves, connected particles and rough planes 6 min
- Work and energy on slopes, with an engine and with friction 6 min
Also for A Level Maths 9709 Paper 4
Which topics come up most in A Level Maths 9709 Paper 4 past papers, counted from every paper since 2004.