MACHINES AND FRICTION

Back to: PRIMARY SEVEN P7 SCIENCE TOPICAL QUESTIONS AND ANSWERS

MACHINES AND FRICTION
Qn. What is a machine?

• A machine is a device that simplifies work.
  Qn. Give the different ways how machines simplify work
• By increasing the speed of doing work.
• By reducing the effort needed to do work.
• By changing the direction of force.
  Qn. State the advantages of using machines.
• Machines increase the speed of doing work.
• Machines reduce the effort needed to do work.
• Machines change the direction of force.
• Machines enable us to apply force easily.
  Work
  Qn. What is work?
• Work is the product of force and distance moved in the direction of force.
  Force
  Qn. What is force?
• Force is a pull or push on an object.
• Force is measured in Newton’s
  Work done
  Qn. What is work done?
• Work done is when a force is used to move a load through a distance.
  Qn. When is work done?
• Work is done when force is used to move another force through a distance.
  Or.
• Work is done when a force is used to move the load through a distance.
  Note:
• Work done depends on two things i.e.
  i) The force applied ii) The distance moved

Work done = force x Distance
WD = F x D

Qn. In which unit is work done measured?

• Joules (J)

Qn. What is a joule?

• A joule is the work done when a force of 1Newton is moved through a distance of 1 metre.
  Note:
  1kg = 10Newtons

Power
Qn. What is power?

• Power is the rate at which work is done.
  Qn. In which units is power measured?
• Power is measured in watts (W)
  Distance
  Qn. What is distance?
• Distance is the length through which an object moves when work is done.
• Distance is measured in metres (M)
  Calculations on work done
  Examples

1. Find the work done by a man who carries a log of wood of 25N through a distance of 7m.

Solution:

Work done = Force x Distance

WD = F X D

WD = 25 X 7 joules

WD = 175 joules

2. A woman carries a baby of 6kg through a distance of 9m.Find the work done.
   Solution

If Musa pushed a wheel barrow of 320 Joules through a distance of 8m, how much force did he use?

4. Find the distance moved by Suzan who carried a basket of 450 joules using an effort of 5kg.
   Solution

Activity:

1. Find the work done by Joshua who lifted a basket of mangoes using a force of 65N through a distance of 5m.
2. Calculate the work done by Otim who pushed a load of 75kg through a distance of 4 metres.
3. Find the force needed by Aisha to push a box of 280 joules through a distance of 7 metres.
4. Samuel pushed a log of wood of 600 joules through a distance of 10m. Calculate the force he used.
   Note:
   1kg = 10N
   5kg = (5 x 10)N
   5kg = 50N
5. Find the distance covered by Shukra if she pushes a load of 30N to do work of 900 joules.
   If stone of 80N is lifted through a certain distance, the amount of work done is 720 joules. Find the distance through which the stone is lifted.
   Types of machines
   Qn. Identify the two types of machines.

• Complex machines
• Simple machines
  a) Complex machines
  Qn. What are complex machines?
• Complex machine are machines that are made up of many parts and need training to use them.
  Qn. Give the examples of complex machines.
• Tractors
• Vehicles
• Sewing machines
• Aeroplane