WORK, POWER AND ENERGY; IMPULSE AND MOMENTUM

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

1. 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
2. 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
3. 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
4. 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

1. impulse on the body a) 120Ns b) 240Ns c) 3.2Ns d) 12Ns
2. final speed of the body a) 1.5m/s b) 2.5m/s c) 2.0m/s d) 3m/s
3. distance covered within the time interval a) 3m b) 30m c) 0.3m d) 0.354m
4. kinetic energy possessed by the body a) 6J b) 9J c) 12J d) 15J
5. power of the body a) 50W b) 22.5W c) 45W d) 12.5W

THEORY

1. 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.
2. 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.