Physics Test 2- chapter 7

A person carries a mass of 10 kg and walks along the +x-axis for a distance of 100 m with a constant velocity of 2 m/s. What is the work done by this person? A) 0 J B) 20 J C) 200 J D) 1000 J E) None of the other choices is correct.

A) 0 J

A simple pendulum, consisting of a mass m and a string of length L, swings upward, making an angle θ with the vertical. The work done by the tension force is A) zero. B) mgL. C) mgL cos θ. D) mgL sin θ. E) mgL tan θ.

A) zero.

Work done by STATIC FRICTION is always A) parallel to the surface. B) perpendicular to the surface. C) positive. D) negative. E) zero.

E) zero.

A constant force is applied to an object that causes a certain displacement. If the angle between the force and the displacement is 135°, the work done by this force is A) positive. B) negative. C) 0 J. D) Cannot be determined without knowing the magnitude of the displacement. E) Cannot be determined without knowing the magnitude of the applied force.

B) negative.

If the net work done on an object is positive, then the object's kinetic energy A) decreases. B) remains the same. C) increases. D) is zero. E) cannot be determined without knowing the object mass.

C) increases.

A person applies a constant force of 20 N to a rock of mass 1000 kg, for a total of 20 seconds. What is the work done by this person if the rock does not move at all by this applied force? A) 1000 J B) 2000 J C) 20,000 J D) 0 J E) 400 J

D) 0 J

A person applies a constant force on an object of mass 20 kg that causes the object to move horizontally at a constant speed of 0.20 m/s through a distance of 0.80 m. What is the work done on the object? A) 160 J B) 10 J C) 16 J D) 0 J E) Cannot be determined without knowing the magnitude of the applied force.

D) 0 J

If you walk 5.0 m horizontally forward at a constant velocity carrying a 10 N object, the amount of work you do is A) more than 50 J. B) equal to 50 J. C) less than 50 J, but more than 0 J. D) zero.

D) zero.

Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do. A) Joel does 75% more work than Jerry. B) Joel does 50% more work than Jerry. C) Jerry does 50% more work than Joel. D) Joel does 25% more work than Jerry. E) Neither of them do any work.

E) Neither of them do any work.

Can work be done on a system if there is no motion? A) Yes, since motion is only relative. B) Yes, if the sum of the external forces is zero. C) Yes, if an external force is acting on the system. D) No, since a system which is not moving has no energy. E) No, since work involves a non-zero displacement.

E) No, since work involves a non-zero displacement.

If you push twice as hard against a stationary brick wall, the amount of work you do A) quadruples. B) doubles. C) is cut in half. D) remains constant but non-zero. E) remains constant at zero.

E) remains constant at zero.

Kinetic energy is proportional to speed.

FALSE

Power is a vector quantity

FALSE

The kinetic energy of an object increases linearly as the velocity of the object increases.

FALSE

The work required to stretch a spring changes linearly with the amount of stretch.

FALSE

Work is a vector quantity.

FALSE

Kinetic energy is a scalar quantity.

TRUE

Kinetic energy is proportional to mass.

TRUE

Work done by a force on an object can be a positive or a negative quantity.

TRUE

State the work-energy theorem

The total work done on (or by) an object is equal to the change in its kinetic energy.