Work
If the point of application of a force is displaced, the force is said to do work. For a constant force F, whose point of application is given a displacement d, work done is the product of /F/ and d.
The work done by a constant force is defined as the product of the force and the distance moved by its point of application along the line of application of the force.
W= / f/d
Power
Power is the rate at which work is being done. For example, if work of 90j is done in 15 seconds, the power is 6J/sec. The unit of power is the Watt (W)
Potential energy
Potential energy of a particle of mass m is the energy of the particle, by virtue of its position relative to a reference level. It is the work done in bringing a particle from a reference level to a height h
If we donate the potential energy by Ek then Ep = 𝐹 × 𝑠
Since F = mg, and S = /
Ep= mgh
Law of Conversation of Energy
This is a generalization if the experience from nature and it state that energy cannot be created nor destroyed. It can only be changed from one from to another
When a particle falls from a height, it loses potential energy. This loss in potential energy is compensated for, in the gain in kinetic energy
GENERAL EVALUATION
- A body of mass 20kg moves a distance of 8m in the direction of line of action of force F =5N on a smooth table find the work done
- A particle of mass 3kg is projected vertically upward with an initial velocity of 5 m/s from the ground, calculate the potential energy at the greatest height
- A sphere of mass 12kg and another sphere of 8kg moves toward each other with velocities 5 m/s and 3 m/s respectively find the speed of the sphere after collision
- Calculate the loss in kinetic energy caused by the collision of the two bodies above in (3)
Reading Assignment
New Further Maths Project 2 page 245 – 257
WEEKEND ASSIGNMENT
A body at rest and of mass 8kg is acted upon by a force of 30N for 0.4 seconds, calculate the
- impulse on the body a) 120Ns b) 240Ns c) 3.2Ns d) 12Ns
- final speed of the body a) 1.5m/s b) 2.5m/s c) 2.0m/s d) 3m/s
- distance covered within the time interval a) 3m b) 30m c) 0.3m d) 0.354m
- kinetic energy possessed by the body a) 6J b) 9J c) 12J d) 15J
- power of the body a) 50W b) 22.5W c) 45W d) 12.5W
THEORY
- A body of mass 6kg moves with speed 3m/s , if it is acted upon by a force of 18N for 4 seconds find the speed of the body.
- The resistance to the motion of a cart being pushed by a man is 220N, if the man pushed the cart a distance of 10km for 45 mins calculate (i) the work done by the man (ii) power exerted by the man.