# FIRST PERIODICAL EXAM Science8

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9. Which of Newton's laws is illustrated when a magician pulls a tablecloth out from under the dishes without disturbing them? a. 1st b. nd 2 c. 3rd d. 2 and 3 10. Newton's third law states that any action will have a(n) _______ and ______ reaction a. Equal and similar c. Equal and opposite b. Equal and different d. Greater and opposite 11. A book is lying at rest on a table. The book will remain there at rest because a. there is a net force but the book has too much inertia b. there is no net force on the book c. there are no forces acting on it at all d. there is a net force, but the book is too heavy to move 12. A hockey puck slides on ice at constant velocity. What is the net force acting on the puck? a. equal to its weight b. less than its weight but more than zero c. zero d. depends on the speed of the puck 13. Unit of mass a. m/s2 c. m/s b. newtons d. kg 14. Which type of force(s) will cause a change in an object’s motion? a. gravity c. zero net force b. balanced forces d. unbalanced forces 15. What is Newton’s First Law known as? The law of a. Friction c. Mass b. Inertia d. Gravity 16. Lighter objects have lesser inertia than heavier objects. a. True b. False 17. _______ is a force that occurs when an object rubs against another object. a. Motion c. Friction b. Velocity d. Speed 18. Which one needs a greater net force to move, a kilogram of feathers or a kilogram of iron? a. feathers c. iron b. same d. depends on their friction 19. You kick a smooth flat stone out on a frozen lake. The stone slides, slows down and eventually stops. You conclude that a. no net force acted on the stone b. the stone has a natural tendency to be at rest c. a net force acted on it all along d. the force pushing the stone forward finally stopped pushing on it 20. Object X has twice the mass of Object Y. Both objects are accelerating at the same rate. Which statement best describes the motions of Object X and Object Y. a. Object X is travelling at twice the speed as Object Y.

b. Object X requires twice the force to accelerate at the same rate as Object Y. c. Object X is travelling at half the speed as Object Y. d. Object X requires half the force to accelerate at the same rate as Object Y. 21. Calculate the centripetal force required to make a 5 kg ball move 4 m/s in a circle with a radius of 2m. 22. What’s the centripetal force of a 0.2 kg yoyo spin in a circle with a radius of 0.7 meters at a velocity of 3m/s? 23. An object with a mass of 0.75kg is whirled in a horizontal circle with a radius of 1.5 m. It makes 3 revolutions in 2 seconds, find it’s (a) constant linear speed, (b) centripetal acceleration and (c) centripetal force.