Forces: Answers
A lorry travels down the motorway with a driving force of 5000 N. If there is 350 N of friction between the lorry and the road, what is the resultant force?
When two forces are acting in opposite directions, the resultant force is the difference between the two forces. 5000 - 350 = 4650 N.
Calculate the weight of a 80 kg man on both the Earth and the moon. The gravitational field strength is 10 N/kg on Earth and 1.6 N/kg on the moon.
Weight = mass x gravitational field strength.
His weight on Earth would be 80 x 10 = 800 N.
His weight on the moon would be 80 x 1.6 = 128 N.
Which factors affect the stopping distance of a car?
The distance travelled when coming to a stop (stopping distance) depends on how quickly we react (thinking distance) and how easily the car can come to a stop (breaking distance). Factors which affect thinking distance are tiredness, whether the person is distracted (e.g. using a mobile phone) and whether they are under the influence of drugs. Factors which affect breaking distance include the weather conditions on the road and whether the tyres are worn out.
A skydiver jumps out of a plane. Explain how they reach terminal velocity.
When the skydiver jumps out of a plane, the downwards force of gravity will initially be much larger than the upwards force of air resistance, causing the person to accelerate downwards. As they gain speed, the upwards force of air resistance will increase until the forces become equal. At this point there is no resultant force and the skydiver will be travelling at a constant speed. They have reached terminal velocity.
Calculate the force needed to extend a spring by 0.5 meters. Spring constant = 20 N/m.
Force = spring constant x extension
Force = 20 x 0.5
Force = 10 N