Practice Test 2 Review PDF

Practice Test 2 Review 1. A ball with momentum 20 (kg. Meter/sec) strikes a wall at a certain velocity and bounces off at the same speed and same mass. What is its momentum AFTER contact with the wall? 2. (T/F) According to the Newton’s First Law, if the NET force on an object i...

Practice Test 2 Review 1. A ball with momentum 20 (kg. Meter/sec) strikes a wall at a certain velocity and bounces off at the same speed and same mass. What is its momentum AFTER contact with the wall? 2. (T/F) According to the Newton’s First Law, if the NET force on an object is zero and if the object is moving at certain velocity in a straight line, it will continue to travel at the same velocity. 3. Consider the equation F=ma. From this equation we can say that Newton is the same as: a. (kg)(sec)/meter b. (kg)(kg)sec c. (kg)(meter)/sec d. all of the above 4. Two objects are traveling in a straight line (same line) - one object 100 kg traveling 10 meter/ sec EAST and the other object 200 kg is traveling at 5 meter/sec WEST. After they collide, they mere into ONE mass. What is the velocity of the combined mass? 5. (T/F) momentum is always conserved irrespective of the type of collision (elastic or inelastic) 6. A large object, 1000 kg mass requires a force of 100N to just get moving. What is the FRICTION caused by the surface and the object? 7. A stationary ball 10 kg mass explodes into two halves, each 5g mass. One 5 kg pieces goes EAST at 10 meter/ sec. The other piece (also 5kg) will be ejected in _ direction. A. EAST B. WEST C. NORTH D. will not move 8. Two objects are traveling in a straight line (same line)- one object 100kg traveling 10 meter/ sec EAST, and the other object 200kg is traveling at 20 meter/ sec WEST. After they collide, they merge into ONE mass. What is the velocity of the combined mass? 9. In Q8, what is the direction of the motion of the combined mass? 10. What are the units of impulse? A. (Newton) (sec) b. (kg)(meter/sec) c. Newton/kg d. both a and b e. all a, b, and c 11. A force 10N is applied to a mas of 40 kg for 30 seconds and the object did not move. Calculate impulse. a. 400 b. 70 c. 300 d. none of the above 12. (T/F) If ten concurrent forces are in equilibrium, the net force is zero. 13. Figure below shows a child on a roller coaster. Find the velocity of the roller coaster (with child) at position B. Motions starts at position A. (Position B is second hill at 50 meters, while point A sits at 100 meters tall). 14. A stationary object at 10 meters above the ground has potential energy = 100J and kinetic energy = 0 (Zero). It falls to the ground. If the mass of the object is ONE kg, what is tis velocity at the time it hits the ground?  15. 100 N force applied 60 degrees with horizontal, moves the object 1 0meters, what is the work? 16. What is meant by rotational equilibrium? 17. (T/F) An object could be in rotational equilibrium and move at an acceleration in a straight line. 18. (T/F) if two objects have identical momentum, they are moving at the same velocity in the same direction. 19. A force of 10 N applied to a massive object for 10 seconds generates an impulse of _; IF THE OBJECT does not move. 20. Two objects one with mass 1 kg and the other with mass of 10kg, have their NET momentum zero. The objects collide and coalesce together. What is the velocity of the combined mass? Answer key: 1. Momentum after contact with the wall: The momentum of the ball before it strikes the wall is 20 (kg·m/s). Since it bounces off at the same speed but in the opposite direction, the momentum after contact will be -20 (kg·m/s). Answer: -20 kg·m/s (momentum AFTER contact with the wall). 2. True/False - Newton’s First Law: True. According to Newton's First Law, if the net force on an object is zero, it will continue to move at the same velocity in a straight line. Answer: True. 3. Newton’s equivalent from F=ma: Rearranging the equation gives us a = F/m. Thus, units of force (F) in Newtons can be expressed as (kg·m)/s². Therefore, Newton is equivalent to: c. (kg)(meter)/sec² Answer: None of the provided options correctly identifies Newton directly; the correct answer is that Newton (N) = (kg·m)/s², however among the choices, none of them fully represent it. The most relevant option is c. 4. Velocity of the combined mass after collision: Let's denote the eastward momentum as positive, so the momentum of object 1 (100 kg, 10 m/s) is (100 \text{ kg} \times 10 \text{ m/s} = 1000 \text{ kg·m/s}) east.  The momentum of object 2 (200 kg, 5 m/s west) is (200 \text{ kg} \times -5 \text{ m/s} = -1000 \text{ kg·m/s}) (since west is negative). Total momentum before collision is (1000 \text{ kg·m/s} + (-1000 \text{ kg·m/s}) = 0). Thus, the velocity of the combined mass is 0 m/s. Answer: 0 m/s. 5. True/False - Momentum conservation: True. In any collision, the total momentum before the collision equals the total momentum after the collision, regardless of whether the collision is elastic or inelastic. Answer: True. 6. Friction force: By Newton's second law, (F = ma). In this case, the frictional force is equal to the applied force needed to overcome it to get the object moving, which is 100 N. Answer: 100 N. 7. Direction of the second piece after explosion: Since momentum is conserved, the momentum of the first piece traveling east at 10 m/s (5kg) is (5 \text{ kg} \times 10 \text{ m/s} = 50 \text{ kg·m/s}) east. For momentum to be conserved, the second piece must have equal and opposite momentum. Thus, it must move west at (50 \text{ kg·m/s} / 5 \text{ kg} = 10 \text{ m/s}). Answer: B. WEST. 8. Velocity of combined mass after second collision: The momentum of object 1 (100 kg, 10 m/s) is (1000 \text{ kg·m/s}) east, and the momentum of object 2 (200 kg, 20 m/s) is (200 \times -20 = -4000 \text{ kg·m/s}). The total momentum before collision is (1000 + (-4000) = -3000 \text{ kg·m/s}). The combined mass is (100 + 200 = 300\text{ kg}), so the velocity after collision (v = \frac{-3000}{300} = -10 \text{ m/s}) (west). Answer: -10 m/s (or west). 9. Direction of combined mass after second collision: Since we calculated a velocity of -10 m/s, the direction of motion will be west. Answer: WEST. 10. Units of impulse: Impulse is defined as the change in momentum, and it is calculated as F*t (force multiplied by time). The unit can be expressed as (N·s) which is equivalent to (kg·m/s). Therefore, the correct unit of impulse is: d. both a and b. Because both (N·s) and (kg·m/s) represent impulse. Answer: d. both a and b.  11. Impulse when the object does not move: If an object does not move, its velocity does not change, creating no impulse (Impulse = change in momentum). Therefore, the impulse is 0 N·s (since impulse = 0 if there is no movement). Answer: Impulse = 0. 12. Velocity of combined mass with zero net momentum: If the net momentum is zero for two objects before they collide, then after they coalesce, the momentum is still zero, which means the combined mass has a velocity of 0 m/s. Answer: 0 m/s. 13. To find the velocity at position B, we can use the conservation of mechanical energy principle. The total mechanical energy (potential energy + kinetic energy) remains constant if only conservative forces (like gravity) are acting. At position A (height = 100 m): Potential Energy (PE_A) = m * g * h_A = (m)(9.8 m/s²)(100 m) Kinetic Energy (KE_A) = 0 (since the motion starts, initial velocity is 0) At position B (height = 50 m): Potential Energy (PE_B) = m * g * h_B = (m)(9.8 m/s²)(50 m) Let (v_B) be the velocity at position B. Then, KE_B = (1/2)mv_B². 14. 15. Where: F = 100 N d = 10 m (\theta) = 60 degrees Calculating: [ W = 100 \cdot 10 \cdot \cos(60^\circ) ] (\cos(60^\circ) = 0.5): [ W = 1000 \cdot 0.5 = 500 \text{ J} 16. Rotational equilibrium occurs when the sum of all torques acting on an object is zero. This means that the object is not experiencing any net torque and, therefore, does not accelerate rotationally. 17. True/False - Rotational equilibrium and translational acceleration  Statement: An object could be in rotational equilibrium and move at an acceleration in a straight line. Answer: True. An object can be in rotational equilibrium (no net torque acting on it) while experiencing linear acceleration (net force acting on it). 18. True/False - Identical momentum Statement: If two objects have identical momentum, they are moving at the same velocity in the same direction. Answer: False. Two objects can have the same momentum even if they have different masses or are moving in different directions (as long as the product of mass and velocity equals the same momentum). 19. Impulse when the object does not move If a force of 10 N is applied for 10 seconds but the object does not move, impulse is calculated as (Impulse = F \cdot t). However, because the object does not move, the impulse resulting from the effective change in momentum is zero. Answer: Impulse = 0 N·s. 20. Velocity of the combined mass For the two objects (1 kg and 10 kg) with a net momentum of zero: If they have zero net momentum, then after they collide and coalesce, their combined velocity will also be zero. Answer: Velocity of combined mass = 0 m/s.