Concept Review and Enrichment

Name______Class______Date______

Concept Review and Enrichment

Section: Newton's First and Second Laws

1.Interpret the following situations to determine whether an object’s velocity is being altered by an applied force (answer Yes or No).

______a.A batter hits a baseball upward into right field.

______b.A satellite orbits Earth at a constant speed of
7,000 m/s.

______c.A submarine moves due east at a constant speed of 45 m/s.

______d.A falling book lands on the floor with a pre-collision speed of 9 m/s.

2.Calculate the acceleration of an 82 kg couch that is pushed across the floor with an unbalanced force of 21 N.

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3.ApplyNewton’s first and second laws to explain why an object moving in a circular path at a constant speed is undergoing acceleration and has a force exerted on it.

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4.Determine the force needed to accelerate a 1,357 kg car forward at 8.0 m/s2.

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5.Explain why a backward-facing car seat is safer for an infant than a forward-facing car seat during a collision or abrupt stop.

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6.Use the concept of inertia to illustrate why volleyball is not played with a ball that has a mass similar to a bowling ball.

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In the space provided, write the letter of the term or phrase that best completes each statement or best answers each question.

_____7.Which statement illustrates Newton’s first law?

a.A stone will not move unless something pushes or pulls it.

b.A ball rolling across the floor eventually slows down.

c.As a car comes to a stop, the passengers continue to move forward.

d.All of the above

_____8.Which object has the greatest inertia?

a.a tennis ball c. a beach ball

b.a bowling ball d. a volleyball

_____9.What force causes a skater sliding on the ice to gradually slow down?

a.a balanced force c. friction

b.inertia d. acceleration

_____ 10. A seat belt helps you when your car stops suddenly by providing a(n)

a.balanced forward force. c. balanced backward force.

b.unbalanced forward force. d.unbalanced backward force.

_____ 11. One newton is the force that can give a mass of 1 kg an acceleration of

a.1 m/s. b.9.8 m/s. c. 1 m/s2. d.9.8 m/s2.

_____ 12. Which of the following will result in the greatest acceleration?

a.56 N acting on a 1-kg box c.23 N acting on a 2-kg box

b.56 N acting on a 2-kg box d.23 N acting on a 5-kg box

_____ 13. What unbalanced force is needed to give a 976 kg vehicle an acceleration of 2.50 m/s2?

a.3.90  102 N c. 2.44  103 N

b.3.90  102 lb d. 2.44  103 lb

_____ 14. A force of 240.0 N causes an object to accelerate at 3.2 m/s2. What is the mass of the object?

a.0.013 kg b. 75 kg c. 240 kgd. 768 kg

_____ 15. A 0.25 kg steel ball experiences a net force of 1.15 N as it rolls down a ramp. What is the acceleration of the ball?

a.0.29 m/s2 b. 0.90 m/s2 c. 1.4 m/s2 d. 4.6 m/s2

_____ 16. If an equal force is applied to two cars of equal mass, Car A and Car B, Car A will have ______acceleration as (than) Car B.

a.the same b. greaterc. less d.the opposite

Using Force Diagrams

Read the following paragraphs, and complete the exercises below.

A running back in football drives toward the goal line. Will he cross it, be stopped dead in his tracks, or be pushed backwards? Force diagrams will help provide the answer.

Just before the play, a running back is motionless because the forces acting on his body are equal and opposite. The force of gravity pulling him toward the ground is opposite and equal to the force of the ground pushing up on him, so he does not move up or down. This balance of forces can be represented by two arrows of the same size pointing in opposite directions. Balanced forces do not cause a change in motion.

On the other hand, unbalanced forces always cause a change in motion. These forces are also represented by arrows. In this case of unbalanced forces, the arrows are of different length. The greater force is represented by a longer arrow.

Exercises

17.Will the ball carrier cross the goal line in diagram “A”? Explain your answer.

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18.Will the ball carrier cross the goal line in diagram “B”? Explain your answer.

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19.Will the ball carrier cross the goal line in diagram “C”? Explain your answer.

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