By Valentina Tobos  Laurentiu Tobos
Updated on Sep 26, 2011
Review these concepts at: Newton's Laws of Motion Study Guide
Practice Questions
Use the conversion table and the prefixes to work the following examples.
 If you are to measure the mass of the earth, you will end up with 5.98 . 10^{24} kg. Rewrite the mass in grams.
 Does a 40 kg piece of furniture have more or less inertia than a 10 kg one? Explain briefly.
 Does a 4,000 μg object have more or less inertia than a 10 kg object? Explain briefly.
 A car starts from a traffic light and accelerates about 1 minute. Is this a uniform linear motion? Explain briefly.
 In the example in the previous problem, is there a resultant force on the object? Explain briefly.
 While driving on the highway with constant speed, the net force on your car is zero. Will your car remain at uniform linear motion if you turn off the engine?
 If the acceleration of an object is zero, does it mean there are no forces acting on the object? Explain briefly.
 If the net force on an object is zero, can the object move with increasing speed? Explain briefly.
 If the net force on an object is zero, is the object necessarily moving in a uniform linear motion? Explain briefly.
 If the net force on an object is directed to the northwest, can we assume that the velocity is also in the NW direction at all times? Explain briefly.
 For a given net force, can we assume that the larger the mass of an object means the larger the acceleration will be? Explain briefly.
 A car of mass 2,000 kg starts from rest and travels 10 m in 2 s. What are the values of the acceleration, assuming uniform acceleration, and of the net force?
 An object moves in the xy plane with an acceleration having components of a_{x} = 1.00 m/s^{2} and a_{y}= 9.80 m/s^{2}. What are the components of the net force if the object has a 0.500 kg mass?
 In practice problem 8, find the acceleration and resultant force.
 In practice problem 8, find the angle of the net force with respect to the y direction.
 Consider two different objects acted upon by the same net force, but one object has a mass the mass of the second object. Find the ratio of the acceleration of the first object with respect to the second object.
 Is it possible to have an object accelerated by a net force in the NW direction while there is a force acting in the SW direction? Explain briefly.
 Consider a puck on the ice (low to no friction) and two hockey players trying to push the puck in opposite directions, with forces of 190 N in the x direction and 250 N in the –x direction. If the puck's mass is 200.0 grams, find the net force and the acceleration.
 \The hockey puck in practice problem 18 is launched by the players and now slides across the ice with constant velocity. What are the net force and acceleration in this example?
 Consider a batteryoperated toy car. If the battery dies, the car will decrease its speed at a rate of 10 cm/s every second (we will consider in this example uniform accelerated motion). Find out the acceleration on the object and the net force if the car's mass is 150 g.
 If a student pulls on a string with a force of 25 N, identify the force of action, the force of reaction, and the value of the two forces. Make sure to explain on which object each of these forces acts.
 Imagine the solar system. Earth acts on the moon with a force we call gravitational force. Does the moon act on the earth? And with what force?
 A solid object and a feather have equal masses. Do they reach the ground in the same amount of time? Explain briefly.
 The two objects in the previous question move, now in vacuum. Do they reach the ground in the same amount of time? Explain briefly.
 Do the two objects in practice problem 23 have to be of equal mass to reach the ground in the same amount of time?
 Consider playing with a medicine ball and you let it fall freely. (These balls can be anywhere between 1 kg and 10 kg. We will consider ours to be 2,500 g.) Draw a diagram for this problem including the vector corresponding to the weight, and then find the value of the weight.
Note: Remember, all vectors are symbolized as arrows pointing in the direction of the motion. An object moving with a constant velocity toward north (consider north to be at the top of the page) will be represented as in Figure 5.3.
 The weight of the same spaceship is different if you measure it on Earth or on another planet by 3:2 ratio. Find out the acceleration due to gravity on the other planet compared with the acceleration due to gravity on Earth
 Consider that a friend is moving. You stack a couple of boxes and would like to find out what is the normal force. One box has a mass of 8 kg and the other has a mass of 12 kg. Draw a freebody diagram and find the normal force.
 Neglecting friction, consider an object on an inclined plane. Also consider pushing down on the object (perpendicular to the surface of the plane). Draw a freebody diagram of the object.
 Consider an object of mass m = 15.0 kg that is pushed by a 20.0 N force at a 30.0° angle with the positive xaxis. Find out the normal force on the object. We will neglect friction.
 In all cases, the normal force exerted by a surface on an object will be equal to the weight of the object? Explain briefly.
 Consider a simple pulley like the one in Figure 5.14. Show all forces acting on the two masses and the pulley. The mass on the left is larger than the mass on the right, and there is no friction between the pulley and the string. The string has negligible mass.
 Consider an object of mass m_{1} = 2.00 kg on an inclined plane of angle 60.0°. There is no friction with the plane. The object is connected with another object through a massless string and a puUey, as in Figure 5.15. Draw the freebody diagram and find the acceleration of the objects for the following cases: (a) m_{2} = 2 kg; (b) m_{2} = 1 kg; and (c) m_{2} = 0.5 kg.
 Consider case (a) in the previous problem and imagine you try to help raise the box up the hill by pushing with a horizontal force on the box of mass m_{1}, as shown in Figure 5.16. What is the new state of motion of the system of the nvo objects?
 You plan to hang a framed picture on the wall, and, because it is a precious family heirloom, you want to take all precautions and find out if the string you have will hold it. The picture has a mass of 2,500 g, and the string can hold up to a tension of 20 N. Considering the final setup similar to the one in Figure 5.17 (a = 45°), find out if your string will have enough strength to support the picture.
 You are moving again, and have tw'o boxes side by side and want to push them out of your way. There is friction with the floor of about 0.8 coefficient of kinetic friction, and the boxes are 12 and 18 kg. You are pushing with a 500 N force horizontally. Find out the acceleration of the system.
 While you are pushing boxes, your back starts hurting, so you proceede to change the position of your body. In the diagram in Figure 5.18, you now apply the force at an angle of 60° with the vertical (see Figure 5.19). Calculate once again the acceleration of the boxes.

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From Physics Success in 20 Minutes A Day. Copyright © 2006 by LearningExpress, LLC. All Rights Reserved.
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