MOTION, WORK AND POWER.

Speed is the distance moved per unit time.

Speed = distance/time.

The speed triangle.

Many speed problems can be solved using the speed triangle. (Think of Eat my dust!)

The following examples will show how to use it.

Examples.

Question
A boy walks a distance of 10 km in 5 hours. Calculate his average speed.

Here, we are looking for the speed.
So we cover the letter S.

This gives us D over T.

Answer.

Speed = distance/time = 10/5 = 2 km/hr.

 

Question
A car travels at a speed of 60 km/hr. Calculate the distance it travels in 3 hours..

Here, we are looking for the distance.
So we cover the letter D.

This gives us S by T.

Answer.

distance = speed x time = 60x3 = 180 km..

 

Question
A horse is running at a speed of 12 km/hr. How long will it take to travel 18 km?

Here, we are looking for the time.
So we cover the letter T.

This gives us D over S.

Answer.

time = distance/speed = 18/12 = 1.5 hr.

Click here for some speed questions.

Click here for more difficult speed questions.

Velocity is distance travelled per unit time in a particular direction.

Acceleration is the change in speed per unit time.

The unit of acceleration is the m/s per second or .

Question
A car is travelling at a speed of 10 m/s. It increases its speed to 34 m/s in a time of 8 seconds. Find its acceleration.

Answer.

 

Click here for some acceleration questions.      Click here for answers to the acceleration questions.

Work is done when a force moves something.

Work done = Force x distance moved.

The S.I. unit of work is the joule.

One joule of work is done when a force of 1 N moves a body a distance of 1 m.

The power of a machine is the amount of work it does per second.