RQ7 You are pushing a heavy refrigerator across a kitchen floor. The forces acting on the refrigerator include:

A. gravityB. gravity and your pushingC. gravity, friction from the floor, and your pushingD. gravity, friction from the floor, a normal force from the floor, and your pushing.

Why do heavy objects fall with the same acceleration as lighter objects?

Lecture Quiz: Question 1

Assume a City Bus collides with a small car. The force exerted by the bus on the small car is much larger that the force exerted by the car on the bus.

A. TRUE

B. FALSE

C. Can’t Tell for the information provided

Figure 4.10The chair pushes back on the hand with a force F2 that is equal in size but opposite in direction to the

force F1 exerted by the hand on the chair.

Figure 4.11Two forces, N and W, act on a book resting on a table.

The third-law reaction forces –N and –W act on different objects, the table and the earth.

Question: A car accelerates from a stop. What force is pushing it?

What is the total force on Cart 1? On Cart 2?

m1 = 10 kg

m2 = 8 kg

F = 36 N

a = 2.0 m/s2

LECTURE QUIZ: Question 2

A person weighs 700 N. While standing on a bathroom scale in an elevator, at a certain moment the scale reads 770 N. Which statement must be true:

A. The force of gravity on the person is greater than the force of the scale on the person.

B. The elevator must be moving upwards at about 1.0 m/s.

C. An upwards acceleration of the elevator has increased the force exerted by the scale on the person.

D. The elevator must be moving upwards, since that is the only way to increase the reading of the scale.

E. Since the scale’s force on the person is equal and opposite to the force of the person on the scale, there is no net acceleration.