*a. Which of the following actions would result in a change in the drag force ac
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Question
*a. Which of the following actions would result in a change in the drag force acting on a bacteria moving through water?
I. Increase in the cross sectional area of the bacteria
II. Without changing the volume, increase in the mass of the bacteria
III. Change in the surface properties of the cell membrane to reduce the drag coefficient
A. I only B. II only C. III only D. I and II E. I and III
*b. If a ball is falling towards the center of the Earth under the influence of its weight and no other forces, which of the following must be true according to Newton’s Third Law?
A. The ball’s velocity is unchanging.
B. The ball will exert a force on the Earth when it hits the ground.
C. The ball exerts a force on the Earth that is equal in magnitude and opposite in direction to the ball’s weight.
D. The ball’s apparent weight is the same as its true weight.
E. The ball will have no effect on the Earth, creating neither a force nor an acceleration.
*c. Which of the following objects are NOT in equilibrium?
A. A DNA molecule moving with constant speed in a gel filled test tube that is rotating around in a circle in a centrifuge.
B. A DNA molecule that is being pulled through gel at a constant velocity by an electric force in an electrophoresis experiment.
C. A book sitting on a table that has a weight pulling it down while a normal force from the table pushes up.
D. A car moves down a highway at constant speed in the same direction while the engine provides a force pushing it in the forward direction and the air provides a drag force pushing it in the backward direction.
E. A hot air balloon floats at a constant height above the ground while not moving in any direction while weight pulls it downward and lift from the hot air pulls it upwards.
Explanation / Answer
*a. Which of the following actions would result in a change in the drag force acting on a bacteria moving through water?
as we know Drag Force = Volume of Bacteria * Density of Water
I. Increase in the cross sectional area of the bacteria Correct : as CSA increases Volume increases hence Drag Force also Increases.
II. Without changing the volume, increase in the mass of the bacteria INCORRECT : Not Depens on Mass of Bacteria deoends on Volume only.
III. Change in the surface properties of the cell membrane to reduce the drag coefficient CORRECT : Drag Cofficient is directly proportional to Drag Force.
A. I only B. II only C. III only D. I and II
E. I and III : Correct
*b. If a ball is falling towards the center of the Earth under the influence of its weight and no other forces, which of the following must be true according to Newton’s Third Law?
Formally stated, Newton's third law is: For every action, there is an equal and opposite reaction. The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object.
A. The ball’s velocity is unchanging.
B. The ball will exert a force on the Earth when it hits the ground.
C. The ball exerts a force on the Earth that is equal in magnitude and opposite in direction to the ball’s weight.
D. The ball’s apparent weight is the same as its true weight.
E. The ball will have no effect on the Earth, creating neither a force nor an acceleration.
CORRECT : C, According to Newton's third law.
*c. Which of the following objects are NOT in equilibrium?
For Equilibrium Net force should be ZERO, or we can say net Acceleration must be Zero.
so Velocity and Speed may be Zero or Constant in both cases object will be in equilibrium.
A. A DNA molecule moving with constant speed in a gel filled test tube that is rotating around in a circle in a centrifuge. : INCORRECT : Constant Speed
B. A DNA molecule that is being pulled through gel at a constant velocity by an electric force in an electrophoresis experiment. : INCORRECT : Constant Velocity
C. A book sitting on a table that has a weight pulling it down while a normal force from the table pushes up.
INCORRECT : Normal force balance M*g.
D. A car moves down a highway at constant speed in the same direction while the engine provides a force pushing it in the forward direction and the air provides a drag force pushing it in the backward direction.
INCORRECT : Constant Speed.
E. A hot air balloon floats at a constant height above the ground while not moving in any direction while weight pulls it downward and lift from the hot air pulls it upwards.
CORRECT : As Balloon moving in X and Y direction with some resultant force, Having non uniform velocity.
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