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WHAT IS FRICTION?

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WHAT IS FRICTION? Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. OR FRICTION IS THE FORCE RESISTING THE RELATIVE MOTION OF SURFACES SLIDING AGAINST EACH OTHER.

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**What two factors affect the force due to friction?**

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**What two factors affect the force due to friction?**

CONDITION OF SURFACES FORCE PUSHING SURFACES TOGETHER

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**A bowling ball with a mass of 5**

A bowling ball with a mass of 5.44 kg and a soccer ball with a mass of 0.43 kg are dropped from a 15 m platform. Identify the correct description of the acceleration of the bowling ball and the force with which it hits the ground with respect to the soccer ball. The force of the bowling ball is greater, and its acceleration is greater. The force of the bowling ball is greater, and its acceleration is the same. The force of the bowling ball is the same, and its acceleration is greater. The force of the bowling ball is the same, and its acceleration is the same.

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**A bowling ball with a mass of 5**

A bowling ball with a mass of 5.44 kg and a soccer ball with a mass of 0.43 kg are dropped from a 15 m platform. Identify the correct description of the acceleration of the bowling ball and the force with which it hits the ground with respect to the soccer ball. The force of the bowling ball is greater, and its acceleration is greater. The force of the bowling ball is greater, and its acceleration is the same. The force of the bowling ball is the same, and its acceleration is greater. The force of the bowling ball is the same, and its acceleration is the same.

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**Which of the following might be the effect of an unbalanced force acting on an object?**

An unbalanced force can only cause an object to slow down. An unbalanced force can cause an object to speed up. An unbalanced force can cause an object to speed up, slow down or change direction. An unbalanced force can only cause a change in direction of motion.

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**Which of the following might be the effect of an unbalanced force acting on an object?**

An unbalanced force can only cause an object to slow down. An unbalanced force can cause an object to speed up. An unbalanced force can cause an object to speed up, slow down or change direction. An unbalanced force can only cause a change in direction of motion.

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**A boulder falls from a cliff**

A boulder falls from a cliff. What is its acceleration at the end of 10 seconds? 98 m/s/s 980 m/s/s 9.8 m/s/s 49 m/s/s

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**A boulder falls from a cliff**

A boulder falls from a cliff. What is its acceleration at the end of 10 seconds? 98 m/s/s 980 m/s/s 9.8 m/s/s 49 m/s/s

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**Which of the following is an example of kinetic energy?**

A car not moving A rock resting on a ledge Water falling over a dam A person sitting in a chair

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**Which of the following is an example of kinetic energy?**

A car not moving A rock resting on a ledge Water falling over a dam A person sitting in a chair

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A box receives an acceleration of 5 m/s2 when a force of 20 N is applied. What force must be applied to the box to have the same acceleration if it encounters a 5 N friction force? 25 N 15 N 30 N 10 N

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A box receives an acceleration of 5 m/s2 when a force of 20 N is applied. What force must be applied to the box to have the same acceleration if it encounters a 5 N friction force? 25 N 15 N 30 N 10 N

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**How much potential energy does a 55 kg person gain when she walks to the top of a hill 20 m tall?**

75 J 539 J 1,100 J 10,780 J

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**How much potential energy does a 55 kg person gain when she walks to the top of a hill 20 m tall?**

75 J 539 J 1,100 J 10,780 J

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**An object has a mass of 12. 8 kg and a velocity of 8. 4 m/s**

An object has a mass of 12.8 kg and a velocity of 8.4 m/s. What is the kinetic energy of the object? 53.8 J 107.5 J 451.6 J 903.2 J

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**An object has a mass of 12. 8 kg and a velocity of 8. 4 m/s**

An object has a mass of 12.8 kg and a velocity of 8.4 m/s. What is the kinetic energy of the object? 53.8 J 107.5 J 451.6 J 903.2 J

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**A student moves a box across the floor by exerting 23**

A student moves a box across the floor by exerting 23.3 N of force and doing 47.2 J of work on the box. How far does the student move the box? m m m 4. 1,099.8 m

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**A student moves a box across the floor by exerting 23**

A student moves a box across the floor by exerting 23.3 N of force and doing 47.2 J of work on the box. How far does the student move the box? m m m 4. 1,099.8 m

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**A large rock has a mass of 750 kg. What is its weight?**

76.5 N 740.2 N 759.8 N 7,350 N

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**A large rock has a mass of 750 kg. What is its weight?**

76.5 N 740.2 N 759.8 N 7,350 N

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**A 100 kg student kicks a 1. 5 kg ball with a force of 450 N**

A 100 kg student kicks a 1.5 kg ball with a force of 450 N. What force does the ball apply on the student? 4.5 N 300 N 450 M 675 N

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**A 100 kg student kicks a 1. 5 kg ball with a force of 450 N**

A 100 kg student kicks a 1.5 kg ball with a force of 450 N. What force does the ball apply on the student? 4.5 N 300 N 450 M 675 N

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**What happens to the kinetic energy and gravitational potential energy of a ball during free fall?**

Gravitational potential energy and kinetic energy both increase. Gravitational potential energy and kinetic energy both decrease. Gravitational potential energy decreases, and kinetic energy increases. Gravitational potential energy increases, and kinetic energy decreases.

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**What happens to the kinetic energy and gravitational potential energy of a ball during free fall?**

Gravitational potential energy and kinetic energy both increase. Gravitational potential energy and kinetic energy both decrease. Gravitational potential energy decreases, and kinetic energy increases. Gravitational potential energy increases, and kinetic energy decreases.

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**A student applies a force to a box with a mass of 30 kg**

A student applies a force to a box with a mass of 30 kg. If the student applies the same force to a box with a mass of 15 kg, which best describes the effect on the acceleration of the 15 kg box? It is half the acceleration of the 30 kg box. It is double the acceleration of the 30 kg box. It is the same as the acceleration of the 30 kg box. It is triple the acceleration of the 30 kg box.

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**A student applies a force to a box with a mass of 30 kg**

A student applies a force to a box with a mass of 30 kg. If the student applies the same force to a box with a mass of 15 kg, which best describes the effect on the acceleration of the 15 kg box? It is half the acceleration of the 30 kg box. It is double the acceleration of the 30 kg box. It is the same as the acceleration of the 30 kg box. It is triple the acceleration of the 30 kg box.

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If a 15 N force is applied to a cart to move it a distance of 5 m, how much work is done on the cart? 0.33 J 3 J 15 J 75 J

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If a 15 N force is applied to a cart to move it a distance of 5 m, how much work is done on the cart? 0.33 J 3 J 15 J 75 J

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A ball with a mass of 5 kg is dropped from a resting position 10 m above the ground. What is the potential energy of the ball just before it is dropped? 0 J 49 J 98 J 490 J

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A ball with a mass of 5 kg is dropped from a resting position 10 m above the ground. What is the potential energy of the ball just before it is dropped? 0 J 49 J 98 J 490 J

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**A 1500 kg CAR IS MOVING AT A CONSTANT VELOCITY OF 2. 5 M/S**

A 1500 kg CAR IS MOVING AT A CONSTANT VELOCITY OF 2.5 M/S. HOW MUCH FORCE IS REQUIRED TO KEEP THE CAR MOVING AT THIS VELOCITY? N N 3. 0 N N

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**A 1500 kg CAR IS MOVING AT A CONSTANT VELOCITY OF 2. 5 M/S**

A 1500 kg CAR IS MOVING AT A CONSTANT VELOCITY OF 2.5 M/S. HOW MUCH FORCE IS REQUIRED TO KEEP THE CAR MOVING AT THIS VELOCITY? N N 3. 0 N N

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**WHAT FACTORS DOES GRAVITY DEPEND ON?**

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**WHAT FACTORS DOES GRAVITY DEPEND ON?**

THE MASSES OF THE TWO OBJECTS INVOLVED AND THEIR DISTANCE APART

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**COULD GRAVITY BE HELD RESPONSIBLE FOR TWO PEOPLE FALLING IN LOVE?**

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**COULD GRAVITY BE HELD RESPONSIBLE FOR TWO PEOPLE FALLING IN LOVE?**

PROBABLY NOT. THE MASSES OF THE TWO PEOPLE WOULD BE SO SLIGHT THAT THE FORCE OF GRAVITY WOULD BE ALMOST INSIGNIFICANT COMPARED TO THE FORCE OF GRAVITY EXPERIENCE BY EITHER ONE AND THE EARTH. OF THE FOUR NATURAL FORCES, GRAVITY IS THE WEAKEST.

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WHAT IS A FORCE?

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WHAT IS A FORCE? A PUSH OR A PULL IS FORCE A VECTOR OR A SCALAR QUANTITY?

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WHAT IS A FORCE? A PUSH OR A PULL IS FORCE A VECTOR OR A SCALAR QUANTITY? VECTOR – IT INVOLVES BOTH A MAGNITUDE AND A DIRECTION

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**WHAT UNITS DO WE USE TO MEASURE FORCE IN THE SI SYSTEM?**

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**WHAT UNITS DO WE USE TO MEASURE FORCE IN THE SI SYSTEM?**

NEWTONS – kg/m/sec2

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WHAT IS WORK?

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WHAT IS WORK? A FORCE APPLIED OVER A DISTANCE W = F X D WHAT UNITS DO WE USE TO MEASURE WORK IN THE SI SYSTEM?

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WHAT IS WORK? A FORCE APPLIED OVER A DISTANCE W = F X D WHAT UNITS DO WE USE TO MEASURE WORK IN THE SI SYSTEM? JOULES – NEWTON METER

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**A 70 KG MAN APPLIES A FORCE OF 1000 N AGAINST A WALL**

A 70 KG MAN APPLIES A FORCE OF 1000 N AGAINST A WALL. HOW MUCH WORK DOES HE DO?

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**A 70 KG MAN APPLIES A FORCE OF 1000 N AGAINST A WALL**

A 70 KG MAN APPLIES A FORCE OF 1000 N AGAINST A WALL. HOW MUCH WORK DOES HE DO? ZERO – MOVEMENT HAS TO OCCUR FOR WORK TO BE DONE

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WHAT IS POWER?

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WHAT IS POWER? POWER = WORK/TIME POWER IS A MEASURE OF THE RATE AT WHICH WORK IS DONE WHAT ARE THE UNITS FOR WORK IN THE SI SYSTEM?

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WHAT IS POWER? POWER = WORK/TIME POWER IS A MEASURE OF THE RATE AT WHICH WORK IS DONE WHAT ARE THE UNITS FOR WORK IN THE SI SYSTEM? WATTS

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**WHAT IS THE DIFFERENCE BETWEEN MASS AND WEIGHT?**

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**WHAT IS THE DIFFERENCE BETWEEN MASS AND WEIGHT?**

WEIGHT IS A MEASURE OF THE FORCE WITH WHICH GRAVITY ATTRACTS SOMETHING. MASS IS INDEPENDENT OF GRAVITY. MASS IS A MEASURE OF HOW MUCH MATERIAL SOMETHING CONTAINS.

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**WHAT IS THE WEIGHT OF A LADY WHOSE MASS IS 70 kg?**

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**WHAT IS THE WEIGHT OF A LADY WHOSE MASS IS 70 kg?**

Weight = 70 kg x 9.8 m/sec2 = 686 N

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THE PERSON IN THE PREVIOUS EXAMPLE IS ON MARS, WHICH HAS ¼ THE GRAVITY OF EARTH. WHAT IS HER MASS, AND WHAT IS HER WEIGHT?

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THE PERSON IN THE PREVIOUS EXAMPLE IS ON MARS, WHICH HAS ¼ THE GRAVITY OF EARTH. WHAT IS HER MASS, AND WHAT IS HER WEIGHT? MASS = 70 kg (not affected by gravity) WEIGHT = 70 X ¼ X 9.8 = N

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**WHAT IS THE DIFFERENCE BETWEEN DISTANCE AND DISPLACEMENT?**

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**WHAT IS THE DIFFERENCE BETWEEN DISTANCE AND DISPLACEMENT?**

DISTANCE IS THE ACTUAL DISTANCE TRAVELED. DISPLACEMENT IS THE CHANGE IN POSITION.

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