Force and Motion I

Efficiency The efficiency of a device is defined as the percentage of the energy input that is transformed into useful energy. Example:In the example above, the input power is 100J/s, the desire output power (useful energy) is only 75J/s, the remaining power is lost as undisire output. Therefore, the efficiency of this machine is Efficiency= … Read more

Power Power is the rate at which work is done, which means how fast a work is done. Formula: Example:An electric motor takes 20 s to lift a box of mass 20kg to a height of 1.5 m. Find the amount of work done by the machine and hence find the power of the electric … Read more

During a conversing of energy, Amount of Work Done = Amount of Energy Converted Example:A trolley of 5 kg mass moving against friction of 5 N. Its velocity at A is 4ms-1 and it stops at B after t seconds. What is the work done to overcome friction?Answer:In this case, kinetic energy is converted into … Read more

Energy Energy is defined as the capacity to do work. Work is done when energy is converted from one form to another. The unit of work is Nm or Joule(J)   Gravitational Potential Energy Gravitational potential energy is the energy stored in an object as the result of its vertical position (i.e., height). Formula:   … Read more

Finding Work from Force-Displacement GraphIn a Force-Displacement graph, work done is equal to the area in between the graph and the horizontal axis. Example:The graph above shows the force acting on a trolley of 5 kg mass over a distance of 10 m. Find the work done by the force to move the trolley.Answer:In a Force-Displacement graph, work done … Read more

Work Done Against the Force of Gravity Example:Ranjit runs up a staircase of 35 steps. Each step is 15cm in height. Given that Ranjit’s mass is 45kg, find the work done by Ranjit to reach the top of the staircase. Answer:In this case, Ranjit does work to overcome the gravity. Ranjit’s mass = 45kgVertical height … Read more

Work Work done by a constant force is given by the product of the force and the distance moved in the direction of the force. The unit of Nm(Newton metre) or J(Joule). Work is a scalar quantity. Formula When the direction of force and motion are same, θ = 0o, therefore cosθ = 1Work done, … Read more

Vectors in Equilibrium When 3 vectors are in equilibrium, the resultant vector = 0. After joining all the vectors tail to head, the head of the last vector will join to the tail of the first vector. Forces in equilibrium Forces are in equilibrium means the resultant force in all directions are zero. When the … Read more

Inclined PlaneWeight component along the plane = Wsinθ.Weight component perpendicular to the plane = Wcosθ. Example:A block of mass 2 kg is pulling along a plane by a 20N force as shown in diagram above. Given that the fiction between block and the plane is 2N, find the magnitude of the resultant force parallel to … Read more

Vector ResolutionA vector can be resolve into 2 component which is perpendicular to each others. Example:Diagram above shows a lorry pulling a log with an iron cable. If the tension of the cable is 3000N and the friction between the log and the ground is 500N, find the horizontal force that acting on the log.Answer: … Read more