# Explain the process for determining, based on a free body diagram, whether or not there is a net…

- How can you tell, based on observing an object, that there is a net force acting upon that object?
- Explain the process for determining, based on a free body diagram, whether or not there is a net force acting on an object.
- Based on Newton’s second law, what are the two ways you can increase the acceleration of an object in a given situation?

- Explain, using Newton’s third law, why jumping into the air and throwing an object makes you travel backwards slightly.

- Explain why, when there is an upward acceleration, normal force must be greater than the force of gravity.

- A box is sitting on a ramp, and is not moving because the force of friction is too great. Explain why increasing the steepness of the ramp decreases the force of friction.

**Practice**

- If a 446 Newton force causes a motorcycle to accelerate at a rate of 2.42 , what is the total mass of the motorcycle?

- Grayson is pushing a box across the floor. If the box has a mass of 68.0 kg, and the force of friction is 91.5 N, how much force will Grayson need to exert to accelerate the box at a rate of 1.41 ?

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- Two piano movers are bringing a piano into a home. One mover pushes to the right with a force of 310 N, while the other pulls to the right as well, but with a force of 270 N. The force of friction acts to the left, with a magnitude of 190 N. The piano weighs 2500 N. What is the net force on the piano?

- A 1295 kg car is driving down the road at a constant speed of 24.4 m/s. The engine exerts a 1450 N force northward, what is the sum of all southward forces exerted on the car?

- A 1.15 kg book is at rest on the table. What is the magnitude of the normal force that the table is exerting on the book?

- Shelley is in an elevator that is traveling downward and slowing down at a rate of 0.950 . If Shelley has a mass of 73.2 kg, what is her apparent weight during this period?

- Jonas has a 10.0 kg box, which he places on a scale inside an elevator. When the elevator begins to move, the scale shows that the box weighs 83.4 N. What is the magnitude and direction of the elevator’s acceleration?

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- Kelley and Raul are moving a 95 kg desk to the right. If the coefficient of friction between the desk and the floor is 0.29, what is the force of friction that will oppose the motion of the desk?

- Bina is pushing a box filled with winter clothing into the closet. The box has a mass of 11.4 kg, and when she pushes with a force of 25.9 N, it accelerates at a rate of 0.84. Based on these values, what is the coefficient of friction between the box and the floor of the closet?

- A team of movers are unloading a truck. One of the movers stays in the truck and places the boxes on a ramp, so they slide down to the other members of the team. One box has a mass of 34.9 kg. The mover places the box on the ramp, which is 24.7° below horizontal. If the coefficient of friction between the box and the ramp is 0.211, how quickly will the box accelerate down the ramp?

**Application**

Cory and Kathy are pushing boxes of supplies for the school play up a 34.8° ramp to get them onto the stage. The largest of the boxes has a mass of 85.5 kg.

- What is the normal force that the ramp is exerting on the box?

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- If the coefficient of kinetic friction between the box and the ramp is 0.298, what is the force of friction that opposes Cory and Kathy’s pushing forces?

- Cory is pushing to the right (up the ramp) with a force of 379 N, and Kathy is pushing to the right with a force of 357 N. What is the magnitude of the acceleration of the box?

- Draw the free body diagram for the box when Cory and Kathy are pushing it (using the values from the previous problems).

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