Introduction to Work

The Kinetic Energy of an object changes when

• its final velocity = its initial velocity

• the object accelerates

• no net force acts on the object

• the object moves in constant velocity

Consider this ball with an initial velocity pointing East. If the ball accelerates with direction East, what happens to the velocity of the object?

• The velocity of the object decreases as it moves East

• The velocity of the object remains constant

• The velocity of the object increases as it moves East

• The velocity of the object increases as it moves West

If the acceleration of this ball points to the west,

• the ball will slow down until it comes to a stop, then begin accelerating to the west

• the ball will start speeding up to the west

• the ball will start speeding up to the east

• the ball will move at constant velocity

This box has a westward acceleration. Which of the following statements is true?

• the sum of all forces acting on the box is zero.

• there is only one force acting on the box, and that is directed west.

• the sum of all forces acting on the box is non-zero, and is directed west

• there is only one force acting on the box, and that force is directed East

Man pushes on the 10 kg box with a horizontal force F_P = 10.0 N i (i-hat). If the net force ΣF_x = 8.0 N i, then what is the friction force acting on the box?

• 2.0 N j

• 18.0 N i

• 1.25 N (-i)

• 2.0 N (-i)

At the moment shown in this picture, what is the acceleration of the box along the horizontal?

• 0.4 m/s²

• 0.6 m/s²

• 0.8 m/s²

• 1 m/s²

If the box starts from rest, and F_P and F_s are constant, then what is the final velocity of the box after 2 seconds of pushing?

• 1.6 m/s, East

• 1.8 m/s, East

• 2.0 m/s, East

• 2.2 m/s,East

To the right is a velocity vs time graph for the box. What should the graph look like?

• a horizontal line

• a vertical line

• a line with a positive slope

• a line with a negative slope

What does the area under the graph and above the t-axis represent?

• the work done on the box

• the change in velocity of the box

• the net force acting on the box

• the displacement of the box

Recall that for this problem, the box reached 1.6 m/s in 2 seconds. What is the displacement of the box during that time ?

• 0.8 m

• 1.2 m

• 1.6 m

• 2.0 m