UNIT 4 – PHYSICAL WORLD


Summary questions 1. Copy and complete the sentences.


A ____________ is anything that causes an object to move, change shape or go in a different direction. Forces that must be in direct contact with the object it is moving are called ____________ forces.


If forces are ____________, they cancel each other out and the object moves with constant ____________ and no acceleration. An unbalanced force will cause an object to speed up or ____________ ____________.


2. a. What is the standard unit of force? b. What instrument can be used to measure force in the laboratory?


3. Calculate the force applied when a 50 kg scooter accelerates at 3 m/s2 .


4. A 25 kg brick is pushed along a smooth table (no friction) with a force of 50 N. Calculate the acceleration of the brick.


5. Give three examples of contact forces.


6. a. What is friction? b. State two advantages of friction. c. State two disadvantages of friction.


7. Describe a method to reduce friction between two rough surfaces. 8. Calculate the weight of the following objects on Earth, given gravitational acceleration is 10 m/s2


a. A person with a mass of 30 kg b. A chocolate bar with a mass of 100 g c. A 2 tonne mass d. A 1500 kg car


9. What would the weight of a 2000 kg space shuttle be on the Moon, if the gravitational acceleration is 1.6 m/s2


?


10. a. Explain Hooke’s law. b. What happens to an object when the elastic limit is exceeded?


11. A student gets the following results when they investigate the extension of a spring due to the force applied:


Extension (cm)


Force (N) 2468 10 3


6 9 12 15


12 16


a. Draw a graph to represent this data. b. What would the extension of the spring be, if a 7 N force were applied? c. Calculate what force would be needed to cause the spring to extend to 14 cm. d. Describe the relationship between force and extension up to 10 N. e. What happens when more than 10 N is applied and why do you think this occurs?


14 16.5 :


280 Elements of Science


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