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A pitcher throws a fastball. When the catcher catches it, (a) positive work is done, (b) negative work is done, (c) the net work is zero.
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The work done by a constant force is equal to the product of the magnitude of the displacement and the component of the force parallel to the displacement.
Here,
is the constant force,
is the displacement, and
is the angle between the force and the displacement.
If the force or force component acts in the same direction of the displacement, then the work is said to be positive. If the force or force component acts in the opposite direction of the displacement, then the work is said to be negative.
When the catcher catches the fastball, the force will act in the opposite direction of the displacement to stop the fastball. Hence, the work is said to negative.
Therefore, the options (a) and (c) are wrong and the correct option is (b).
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When walking up stairs, it is easier to do so in a zigzag path rather than going straight up. Why is this ( Hint : Think of an inclined plane.)
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The work done
When we go straight up, the gravitational force makes an angle 180 0 with the displacement. But, if we go in zigzag path it makes less angle with gravitational force. That is why it is easier to go up in a zigzag path than straight.
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A 3.00-kg block slides down a frictionless plane inclined 20° to the horizontal. If the length of the plane's surface is 150 m, how much work is done, and by what force
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Work done is defined as the dot product of force and displacement
Here, F is the force vector and s is the displacement and
is the angle between them.
Consider the following diagram
The only force acting along the motion of block is
, where
is the angle of inclination. Hence this is the only force responsible for the work done.
Angle between the motion and force vector is
Thus, work done by this force is,
Substitute 3 kg for m , 1.5 m for s, 9.8
for g,
and
Hence, the work done is
which is done by component of its weight.
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If a person does 50 J of work in moving a 30-kg box over a 10-m distance on a horizontal surface, what is the minimum force required
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Suppose the coefficient of kinetic friction between the block and the plane in Exercise is 0.275. What would be the net work done in this case
Exercise
A 3.00-kg block slides down a frictionless plane inclined 20° to the horizontal. If the length of the plane's surface is 150 m, how much work is done, and by what force
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A 5.0-kg box slides a 10-m distance on ice. If the coefficient of kinetic friction is 0.20, what is the work done by the friction force
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You are carrying a backpack across campus. What is the work done by your vertical carrying force on the backpack Explain.
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The work done by a variable force of the form F = kx is equal to (a) kx 2 , (b) kx , (c) 
kx 2 , (d) none of the preceding.
kx 2 , (d) none of the preceding. Short Answer
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(a) As a weightlifter lifts a barbell from the floor in the "clean" procedure (Fig. a), has he done work Why or why not (b) In raising the barbell above his head in the "jerk" procedure, is he doing work Explain. (c) In holding the barbell above his head (Fig. b), is he doing more work, less work, or the same amount of work as in lifting the barbell Explain. (d) If the weightlifter drops the barbell, is work done on the barbell Explain what happens in this situation.
FIGURE Man at work See Conceptual.
FIGURE Man at work See Conceptual. Essay
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A father pushes horizontally on his daughter's sled to move it up a snowy incline, as illustrated in Fig. b. If the sled moves up the hill with a constant velocity, how much work is done by the father in moving it from the bottom to the top of the hill (Some necessary data are given in Exercise.)
FIGURE Fun and work See Exercise.
Exercise
A father pulls his young daughter on a sled with a constant velocity on a level surface a distance of 10 m, as illustrated in Fig. a. If the total mass of the sled and the girl is 35 kg and the coefficient of kinetic friction between the sled runners and the snow is 0.20, how much work does the father do
FIGURE Fun and work See Exercise.
FIGURE Fun and work See Exercise.
Exercise
A father pulls his young daughter on a sled with a constant velocity on a level surface a distance of 10 m, as illustrated in Fig. a. If the total mass of the sled and the girl is 35 kg and the coefficient of kinetic friction between the sled runners and the snow is 0.20, how much work does the father do
FIGURE Fun and work See Exercise. Essay
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If a spring is compressed 2.0 cm from its equilibrium position and then compressed an additional 2.0 cm, how much more work is done in the second compression than in the first Explain.
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A jet plane flies in a vertical circular loop. In what regions of the loop is the work done by the force of gravity on the plane positive and/or negative Is the work constant If not, are there maximum and minimum instantaneous values Explain.
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The units of work are (a) N · m, (b) kg · m 2 /s 2 , (c) J, (d) all of the preceding.
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A passenger at an airport pulls a rolling suitcase by its handle. If the force used is 10 N and the handle makes an angle of 25° to the horizontal, what is the work done by the pulling force while the passenger walks 200 m
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For a particular force and displacement, the most work is done when the angle between them is (a) 30°, (b) 60°, (c) 90°, (d) 180°.
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Work done in free fall (a) is only positive, (b) is only negative, or (c) can be either positive or negative.
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Which one of the following has units of work: (a) N , (b) N/s, (c) J · s, or (d) N · m
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Does it take twice the work to stretch a spring 2 cm from its equilibrium position as it does to stretch it 1 cm from its equilibrium position
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A father pulls his young daughter on a sled with a constant velocity on a level surface a distance of 10 m, as illustrated in Fig. a. If the total mass of the sled and the girl is 35 kg and the coefficient of kinetic friction between the sled runners and the snow is 0.20, how much work does the father do
FIGURE Fun and work See Exercises.
FIGURE Fun and work See Exercises. Essay
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