Ch 5: Applying Newton's Laws

Question 1

The definition of apparent weight is the _________ of supporting _______ ______.

Answer 1

magnitude of supporting contact forces

p. 142

Question 2

If you are in equilibrium, your weight and apparent weight are generally the same. But if you undergo an acceleration, this is not necessarily the case. For instance, you feel “_____” when an elevator you are riding in suddenly accelerates upward, and you feel lighter than normal as the upward-moving elevated brakes to a halt.

Now, for a person in an upward-acclerating upward, the sums of forces in the y-direction can be summarized as:

Σ F_y = n_y - w_y = ma_y

If we think of the normal force as his apparent weight, or w_app, what is the formula we would use to calculate his apparent weight?

The apparent weight is greater than the man’s weight w, so he feels heavier than normal. If, instead, the elevator has a downward acceleration, then a_y is -a, so that w_app = _______. The apparent weight is less than the man’s weight, and the man feels lighter than normal.

Answer 2

heavy

w_app = w + ma_y

w_app = w - ma_y

Question 3

In an elevator problem, if the apparent weight is greater than the actual weight, then the acceleration is ________. If less, the acceleration is ________.

Answer 3

upward

downward

Question 4

If an object is slowing, its velocity and acceleration vectors point…

Answer 4

….in opposite directions.

p. 143

Question 5

What is the apparent weight of an object in free fall?

Answer 5

zero

p. 144

Question 6

What is meant by the term “weightless” as applied to object in outer space?

Answer 6

The object or person has no apparent weight.

Question 7

The drag force pushes opposite your motion as you ride a bicycle. If you double your speed, what happens to the magnitude of the drag force?

A. The drag force increases.

B. The drag force stays the same.

C. The drag force decreases.

Answer 7

A. the drag force increases