Force On a Cart is Tripled (Answer Key)

If the net force on a cart is tripled, the cart’s acceleration is A) is one third. B) is two thirds. C) is three times as much. D) is more than three times as much. The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is A) more than 10 N. B) less than 10 N. C) 10 N. A 10-N falling object encounters 4 N of air resistance. The net force on the object is A) 0 N. B) 4 N. C) 6 N. An object's weight is properly expressed in units of A) meters. B) kilograms. C) newtons. D) cubic centimeters. When you stand at rest with your left foot on one bathroom scale and your right foot on a similar scale, each of the scales will A) read half your weight. B) read your weight. C) show readings that when added equal your weight. D) cancel your weight. A constant net force on a railroad car produces constant A) velocity. B) acceleration. C) both of these D) neither of these A car by itself is capable of a certain maximum acceleration. When it tows a twice-as-massive car, its maximum acceleration is A) one half. B) one third. C) one fourth. D) the same. E) none of these A sack of potatoes weighing 200 N falls from an airplane. As the velocity of fall increases, air resistance also increases. When air resistance equals 200 N, the sack's acceleration becomes A) 0 m/s2. B) 10 m/s2. C) infinite. D) none of the above Why does a heavy parachutist fall faster than a lighter parachutist who wears a parachute of the same size? A) Terminal speed must be lower to make air drag equal the gravity force for a heavier person. B) Gravity is greater on the heavier person, so they fall at g. C) Terminal speed must be higher to make air drag equal the gravity force for a heavier person. D) Terminal speed is inversely proportional to the mass of the parachutist. Calculate the weight in newtons of a person having a mass of 40 kg . w = mg w = (40N) (10 m/s2) w = 400N Consider a 38-kg block of cement that is pulled sideways with a net force of 200 N. Calculate its acceleration. a = F/m a = 200N / 38kg a = 5.26 m/s2 A 10-kilogram block is pushed across a horizontal surface with a horizontal force of 20 N against a friction force of 10 N. Calculate the acceleration of the block. a = F/m 20 N - 10N = 10N a = 10N / 10kg a = 1 m/s2 Chapter 5 When you walk, you push on the floor to the left and the floor A) also pushes on you to the left. B) pushes you to the right. C) both of these simultaneously. D) can only wish it could push on you. E) none of the above A car traveling at 100 km/h strikes an unfortunate bug and splatters it. The force of impact is A) greater on the bug. B) greater on the car. C) the same for both. What is Newton’s Third Law? Newton’s Third Law of motion states that for every action, there is an equal and opposite reaction. This reaction force is equal in magnitude and opposite in direction. The force with which Earth pulls on the Moon is A) somewhat greater than Moon's pull on Earth. B) the only force acting between Earth and Moon. C) equal in magnitude to the force that Moon pulls on Earth. When a cannonball is fired from a cannon, which undergoes the greater acceleration? A) the cannonball B) the recoiling cannon C) both the same Chapter 6 Which has the greater momentum when moving? A) a container ship B) a bullet C) a car D) either of these depending on speed The total momentum of a flock of identical birds could be zero only if the birds are A) taking off from the ground. B) flying in the same direction. C) flying in different directions. D) very tired and coming down to rest. To catch a fast-moving ball, you extend your hand forward before contact with the ball and let it ride backward in the direction of the ball's motion. Doing this reduces the force of contact on your hand principally because the A) force of contact is reduced. B) relative velocity is less. C) time of contact is increased. D) time of contact is decreased. E) none of the above Two billiard balls having the same mass and speed roll toward each other. What is their combined momentum after they meet? A) zero B) half the sum of their original momentums C) twice the sum of their original momentums D) need more information What is the momentum of an 8.2-kg bowling ball rolling at 2.2 m/s ? p = mv p = (8.2 kg)(2.2 m/s2) p = 18.04 kg*m/s2 What impulse occurs when an average force of 9.0 N is exerted on a cart for 3.0 s ? I = force * time I = Δ mass / velocity I = 9N * 3s I = 27 kg*m/s2 A 5000-kg freight car collides with a 10,000-kg freight car at rest. They couple upon collision and move at 2 m/s. What was the initial speed of the 5000-kg car? Conservation of momentum: (total p= mv)initial = (total p= mv)final M = 5000 kg freight car = vintital, V = 0 M = 10,000 freight car + 5000 kg freight car = pfinal, V= 0 V = 2 m/s *finding vinitial (5000 kg) = (10,000 kg + 5000 kg)(2 m/s) (5000 kg) = 30,000 kg*m/s Vinitial = 30,000 kg / 5000 kg Vinitial = 6 m/s A 2-kg rifle that is suspended by strings fires a 0.01-kg bullet at 200 m/s. The recoil velocity of the rifle is about A) 0.001 m/s. B) 0.01 m/s. C) 0.1 m/s. D) 1 m/s. 2 kg = (0.01 kg)(200 m/s) 2 kg = 2 kg*m/s Vinitial = 1 m/s A 50 kg fish swimming at .50 m/s swallows an absent minded 1.0 kg fish toward it at a speed that brings both fish to a halt immediately after lunch. Find the speed of the approaching smaller fish before lunch.