فيزياء: أي استفسار أول سؤال

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في شبتر 7

3. A boy holds a 40-N weight at arm’s length for 10 s. His arm is 1.5m above the ground. The
work done by the force of the boy on the weight while he is holding it is:
A. 0
B. 6.1J
C. 40 J
D. 60 J
E. 90 J
Ans:a


5. An object moves in a circle at constant speed. The work done by the centripetal force is zero
because:
A. the displacement for each revolution is zero
B. the average force for each revolution is zero
C. there is no friction
D. the magnitude of the acceleration is zero
E. the centripetal force is perpendicular to the velocity
Ans:e

6. An object of mass 1 g is whirled in a horizontal circle of radius 0.5m at a constant speed of
2m/s. The work done on the object during one revolution is:
A. 0
B. 1 J
C. 2 J
D. 4 J
E. 16 J
ans: A

10. A 2-kg object is moving at 3m/s. A 4-N force is applied in the direction of motion and then
removed after the object has traveled an additional 5m. The work done by this force is:
A. 12 J
B. 15 J
C. 18 J
D. 20 J
E. 38 J
ans: D

13. Camping equipment weighing 6000N is pulled across a frozen lake by means of a horizontal
rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in
pulling the equipment 1000m if its speed is increasing at the constant rate of 0.20m/s2?
A. −1.2 × 106 J
B. 1.8 × 105 J
C. 3.0 × 105 J
D. 4.2 × 105 J
E. 1.2 × 106 J
ans: D

14. A 1-kg block is lifted vertically 1m by a boy. The work done by the boy is about:
A. 1 ft · lb
B. 1 J
C. 10 J
D. 0.1J
E. zero
ans: C

19. An 80-N crate slides with constant speed a distance of 5.0m downward along a rough slope
that makes an angle of 30◦ with the horizontal. The work done by the force of gravity is:
A. −400 J
B. −200 J
C. −69 J
D. 200 J
E. 400 J
ans: D

21. A man wishes to pull a crate 15m across a rough floor by exerting a force of 100 N. The
coefficient of kinetic friction is 0.25. For the man to do the least work, the angle between the
force and the horizontal should be:
A. 0
B. 14◦
C. 43◦
D. 66◦
E. 76◦
ans: A