If you push with 200 N of force against your 1500-N refrigerator and it slides across your kitchen floor at constant velocity, friction of the floor against the refrigerator must be
1) zero,
2) 200 N,
3) 1300 N,
4) 1500 N,
5) greater than 1500 N,
and the force with which you push must be
6) equal and oppositely directed to the friction force.
7) the action force, and the friction the reaction force.
8) both of these.
9) none of these.
[Ques. 2] While a ship moves toward the right at constant velocity, a seaman atop the mast drops a stone which freely falls to position
1) A.
2) B.
3) C.
This is better understood by realizing that
4) the ship moved to the right a distance equal to that between A and B while the stone fell vertically.
5) the stone was moving to the right just as fast as the ship during the fall.
6) the net force acting on the stone is equal to its weight.
7) because of inertia, the stone experiences a horizontal motion unlike that of the ship.
8) the stone underwent an acceleration while the ship did not.
[Ques. 3] Two 50-N weights pull on the scale as shown. The reading on the scale is
1) 0 N.
2) 25 N.
3) 50 N.
4) 100 N.
This is clearer to understand if we think of the situation this way:
5) Since no acceleration is taking place, the forces cancel one another.
6) One of the weights holds the scale while the other weight stretches the spring.
7) The two hanging weights provide forces that constitute an action/reaction pair.
[Ques. 4] The two men compete in a tug of war. Both pull equally and the scale reads 800 newtons. Each man must pull with a force of
1) 400 N.
2) 800 N.
3) 0 N.
Consider action and reaction forces in this case: If action is the man on the left pulling on the rope, then the reaction force is
4) the rope pulling on the man on the left.
5) the rope pulling on the man on the right.
6) the man on the right pulling on the rope.
[Ques. 5] Each group in a tug-of-war pulls with 1000 N on each side of the rope. The net force on the rope is
1) 0 N
2) 500 N
3) 1000 N
4) 2000 N
and the tension within the rope is
5) 0 N.
6) 500 N.
7) 1000 N.
8) 2000 N.
[Ques. 6] If an 800-N man hangs motionless from four vertical strands of rope, then the tension in each strand of rope is
1) 0 N
2) 200 N
3) 400 N
4) 800 N
which results in a net force on the man of
5) 0 N.
6) 200 N.
7) 400 N.
8) 800 N.
[Ques. 7] A 100-N little physics tyke hangs on the ends of a rope suspended over a pulley as shown. The tension in the rope is
1) 0 N.
2) 50 N.
3) 100 N.
4) 200 N.
It is interesting to note that
5) the tension in the rope at its midpoint (uppermost part) is 100 N.
6) this is a modified tug-o'-war example (simply draped over a pulley).
7) the net force acting on the rope is in this case identical to the child's weight.
[Ques. 8] You can exert more force on the pedals of a bicycle if you pull up on the handlebars because
1) your center of gravity can be shifted to a position directly above the pedals,
2) the handlebars, in turn, pull down on you and this force is transmitted to the pedals,
3) rotational inertia is lessened,
4) rotational inertia is increased,
all of which illustrates
5) that equilibrium is center-of-gravity dependent.
6) the law of action and reaction.
7) inertia may be both linear and rotational.
[Ques. 9] Which of the following has the greater weight?
1) 1 kilogram of gold
2) 1 kilogram of feathers
3) both weigh the same in the same locality
This follows from the fact that
4) gold is more compact than feathers.
5) weight and mass are directly proportional to each other.
[Ques. 10] If an object has twice as much mass as another, then it also has twice as much
1) acceleration.
2) weight.
3) center of gravity.
4) area.
This is because
5) of inertia.
6) mass and weight are directly proportional to each other.
7) the gravitational force acting on all objects in the same locality is the same.
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