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

19) A child weighs 293 N. What is the child's mass in kilograms? What is the child's mass in slugs?

20) The mass of a certain elephant is 3,067 kg. a. Find the elephant's weight in newtons

b. Find its weight in pounds.

21) A motorcycle and rider have a total mass equal to 315 kg. The rider applies the brakes, causing the motorcycle to accelerate at a rate of 2 m/s². What is the net force on the motorcycle? (Indicate the direction with the sign of your answer.)

22) The Kingda Ka roller coaster in New Jersey is the world's tallest ride of its kind. As the passenger cars are launched from rest at the start, they are accelerated uniformly to a speed of 57 m/s (128 mph) in just 3.5 s. (Assume the cars are launched in the positive horizontal direction. Indicate the direction with the sign of your answer where appropriate.)

a. What is the acceleration experienced by passengers on this ride in m/s²?

b. What is the acceleration experienced by passengers on this ride in g's?

c. If a certain passenger has a mass of 61 kg, what is the force in newtons that acts on him during the launch phase of this ride?

d. What is the force in pounds that acts on him during the launch phase of this ride?

23) A jet aircraft with a mass of 4,675 kg has an engine that exerts a force (thrust) equal to 59,300 N. a. What is the jet's acceleration when it takes off? (Give the magnitude.) b. What is the jet's speed after it accelerates for 9 s? (Assume it starts from rest.) c. How far does the jet travel during the 9 s?

24) A race car rounds a curve at 59 m/s. The radius of the curve is 435 m, and the car's mass is 615 kg. (Assume the car's speed remains constant. Take the radially inward direction to be positive. Indicate the direction with the sign of your answer.) a. What is the car's (centripetal) acceleration?

b. What is it in g's?

c. What is the centripetal force acting on the car?

25) A centripetal force of 225 N acts on a 1,050-kg satellite moving with a speed of 5,200 m/s in a circular orbit around a planet. What is the radius of its orbit?