2nd Midterm

John Smith, a strongman competitor, lifts a 400 kg barbell to a height of 1.2 meters. What is the work done by John in lifting the barbell?

• A. 400 J

• B. 4900 J

• C. 4704 J

• D. 4800 W

Answer explanation

Work is calculated using the formula:

W=F×d

Where F=mg and d is the height lifted.

Given:

• m=400 kg

• g=9.8 m/s2

• d=1.2 m

First, calculate the force:

F=400 kg×9.8 m/s2=3920 N

Now, calculate the work:

W=3920 N×1.2 m=4704 J

What happens when the force applied and the displacement are at an angle to each other?

• A. No work is done unless the force is entirely parallel.
  

• B. The entire force contributes to the work done.
  

• C. Only the component of the force perpendicular to the displacement does work.
  

• D. Only the component of the force parallel to the displacement does work.

Which of the following is an example of work done?

• A. You push a shopping cart but it doesn’t move.

• B. You carry a backpack while walking down the street.

• C. You lift a box and place it on a shelf.

• D. You sit still and read a book.

Answer explanation

In this case, work is done because force is applied to the box, causing it to move through a distance.

How much work does Sam perform while lifting a 5-N book vertically through a height of 3 meters?

• A. 15 J
  

• B. 10 J
  

• C. 5 J
  

• D. 0 J

How is the work done on an object by a constant force described?

• A. The force divided by the distance.
  

• B. The product of the force and the distance the object moves in the direction of the force.
  

• C. The force added to the displacement of the object.
  

• D. The difference between the displacement and the force.

At a factory, workers operate a crane to lift heavy boxes onto a shelf. The crane's motor is powered by electricity, which turns the motor's gears. In this situation, the motor converts ________ into ________.

• A. Kinetic Energy, Electrical Energy
  

• B. Electrical Energy, Kinetic Energy
  

• C. Electrical Energy, Chemical Energy
  

• D. Gravitational Potential Energy, Solar Energy

A 5-kg ball is held 15 meters above the ground. How much potential energy does the ball have?

• A. 735 J
  

• B. 750 J
  

• C. 490 J
  

• D. 600 J

Which of the following statements about potential energy is TRUE?

• A. Potential energy depends only on the mass of the object.
  

• B. Potential energy is independent of the height of the object.
  

• C. The higher an object is, the less potential energy it has.
  

• D. Potential energy is the energy an object possesses because of its position or condition.

Which of the following statements about kinetic energy is TRUE?

• A. Kinetic energy depends only on the object’s mass.
  

• B. Kinetic energy depends on how fast the object is moving.
  

• C. Kinetic energy increases as the object’s size increases.
  

• D. Kinetic energy is unaffected by the object's speed.

Power is the rate at which work is done or energy is transferred. What is the unit for power?

• A. J
  

• B. W
  

• C. N m
  

• D. kg m/s