If an object of mass m moves with constant velocity v, the net force on the object is（）
A. mg
B. mv
C. mv/t
D. 0
E. None of these answers is correct
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Alex and John are loading identical cabinets onto a truck. Alex lifts his cabinet straight up from theground to the bed of the truck, whereas John slides his cabinet up a rough ramp to the truck. Whic
Alex and John do the same amount of work
B. Alex does more work than John
C. John does more work than Alex
D. None of those statements is necessarily true because the angle of the incline is unknown
Which one of the following statements is true concerning the motion of an ideal projectile launched at an angle of 45°to the horizontal（）
A. The acceleration vector points opposite to the velocity vector on the way up and in the same direction as the velocity vector on the way down
B. The speed at the top of the trajectory is zero
C. The object’s total speed remains constant during the entire flight
D. The horizontal speed decreases on the way up and increases on the way down
E. The vertical speed decreases on the way up and increases on the way down
The radial component of velocity for a particle moving in a circular path is____（）
A non-zero constant
B. Radius itself
C. Variable
D. Zero
Which of the following is a scalar quantity（）
A. speed
B. time
C. length
D. instantaneous acceleration
E. instantaneous velocity
F. average velocity
G. average acceleration
H. magnitude of position vector
I. none of the above
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