2) Two children pull on a sled, one to the left with a force of 20 N and the other to the right with a force of 25 N. Consider the force of friction small enough to ignore. What is the net force acting on the sled?

a. The net force is zero, since the children are pulling in opposite directions.

b. The net force is 45 N to the right, because that is the total amount of force applied to the sled.

c. The net force is 25 N to the right, since that is the largest force.

d. The net force is 5 N to the right, since the force to the right is larger in magnitude than the force to the left

.

7) If a 0.3 kg object hanging from a spring stretches it by 0.15 m, then by how much will the spring be stretched (in m) if a 0.6 kg object is suspended from it?

9) Suppose an airline allows a maximum of 25 kg for each suitcase a passenger brings along.

a. What is the weight in newtons of a 25 kg suitcase?

b. What is the weight in pounds?

10) The mass of a subway car and passengers is 48,400 kg. If its acceleration as it leaves a station is 0.6 m/s², what is the net force (in N) acting on it? (Enter the magnitude.)

11) In an experiment performed in a space station, a force of 91 N causes an object to have an acceleration equal to 2 m/s². What is the object's mass?

12) A person stands on a scale inside an elevator at rest (see the figure below). The scale reads W = 614 N. a. What is the person's mass? b. The elevator accelerates upward momentarily at the rate of a = 4 m/s². What does the scale read then? c. The elevator then moves with a steady speed of 4 m/s. What does the scale read now?

13) On aircraft carriers, catapults are used to accelerate jet aircraft to flight speeds in a short distance. One such catapult takes a 18,100-kg jet from 0 to 66 m/s in 2.8 s. (Assume the catapult acts in the positive horizontal direction. Indicate the direction with the sign of your answer where appropriate.)

a. What is the acceleration of the jet in m/s²?

b. What is the acceleration of the jet in g's?

c. How far does the jet travel while it is accelerating?

d. How large is the force that the catapult must exert on the jet?

14) On a highway curve with radius 30 m, the maximum force of static friction (centripetal force) that can act on a 1,223-kg car going around the curve is 9,127 N. What speed limit should be posted for the curve so that cars can negotiate it safely?

15) A space probe is launched from Earth headed for deep space. At a distance of 10,000 miles from Earth's center, the gravitational force on it is 890 lb. What is the size of the force when it is at each of the following distances from Earth's center? a. 20,000 miles

b. 30,000 miles

c. 100,000 miles