Ch 2 – Newton’s 1st Law (Inertia) QUIZ Review

ANSWERS

1) A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked quickly. This best demonstrates what about the milk carton?

ANSWER: the milk carton has inertia. Inertia of rest.

2) An object in mechanical equilibrium is an object (careful - thinking question)

A. If it is at rest (Not moving).

B. If the object is moving with constant velocity

(same speed) and has no acceleration.

3) When you stand at rest on a pair of bathroom scales, the readings on the scales will always

Answer: add up to equal your weight.

4) Hang from a pair of gym rings and the upward support forces of the rings will always

ANSWER: add up to equal your weight.

5) A man weighing 800 N stands at rest on two bathroom scales so that his weight is distributed evenly over both scales. The reading on each scale is

ANSWER: 400 N.

What if the man is on all fours, 2 hands and 2 feet on 4 different scales?

ANSWER: 200 N

6) The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is

ANSWER: 10 N.

A. What happens if you apply more than 10 N force?

ANSWER: The object speeds up.

B. What happens if you reduce the friction to less than 10 N?

ANSWER: The object speeds up.

7) A 200-kg bear grasping a vertical tree slides down at constant velocity. The friction force between the tree and the bear is

A. The friction force (in Newtons) between the tree and the bear is? (Hint:1 kg X 10 m/sec2 = 10 Newtons)

Math required to solve the problem: 200 kg X 10 m/sec2 = ANSWER: 2000 Newtons

B. How much does the bear weigh in pounds? Hint 2.2 lb./kg

Math to solve the problem: 200 kg X 2.2 lb./kg = 440 lbs

8) A package falls off a truck that is moving at 50 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is

ANSWER: about 50 m/s.

9) A truck is moving at constant velocity. Inside the storage compartment of the truck a rock is dropped from the midpoint of the ceiling and strikes the floor below. Where will the rock hit the floor with reference to the ceiling?

ANSWER: exactly below (underneath) the midpoint of the ceiling.

10) If your automobile runs out of fuel while you are driving, the engine stops but you do not come to an abrupt stop. The concept that most explains why is

ANSWER: inertia.

11) According to Newton's law of inertia, a railroad train in motion should continue going forever even if its engine is turned off. We never observe this because railroad trains

ANSWER: there is always friction that always is forces that oppose their motion.

12) Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the tendency of the rock is to

ANSWER: follow a straight-line path.

13) When a rocket ship accelerating in outer space runs out of fuel, what happens to the rocket’s acceleration?

ANSWER: IT no longer accelerates.

A. What happens to the rockets velocity? Why?

Velocity is pretty much constant if not close to a planet.

B. Why?

No forces are being applied to the rocket ship.

14) If no external forces are acting on a moving object, what happens to the velocity and acceleration?

ANSWER:

Continue moving at the same velocity.

And the acceleration will be zero (no acceleration).