Basic Work and KE

What is the SI unit for work?

• kilogram

• Watt

• Joule

• Newton

A student's pencil falls off their desk and comes to rest on the floor a few feet away. The work done by gravity on the pencil is...

• ... positive since gravity pulls in the same direction as the pencil's displacement.

• ... zero since the pencil begins and ends at rest.

• ... negative since the pencil's direction of motion is down

• ... impossible to determine without knowing the mass of the pencil and height of the desk.

A delivery person boards a stationary elevator, rides it to the top floor, and then gets out. The net work done on the elevator is...

• ... negative, because gravity points in the opposite direction of the displacement.

• ... zero, because the elevator begins and ends at rest.

• ... positive, because the force applied by the cables is in the same direction as the elevator's displacement.

• ... impossible to determine without more information like the rider's mass, height of the building, etc.

A block of mass m slides a distance d down a ramp declined at an angle θ (in degrees) from the horizontal. How much work does gravity do?

• W = mgd cos θ

• W = mgd cos (90 - θ)

• W = -mgd

• W = mgd

Object A has mass m and velocity v. Object B has twice as much mass and travels twice as fast. How does Object A's kinetic energy compare to Object B's?

• Object A has half the kinetic energy of Object B

• Objects A and B have the same kinetic energy

• Object B has four times the kinetic energy of Object A

• Object B has eight times the kinetic energy of Object A

A 10 N block, a 5 N block, and a 1 N block are in contact with one another, ordered left to right. A constant force is applied from the left, and the system slides to the right at constant speed against a constant, net frictional force of 16 N. If the blocks move 2m to the right, what is the work done by the 5 N block on the 1 N block?

• 2 J

• 5 J

• 10 J

• 12 J

• 32J