Two blocks are connected by a thin string The pulley is mass

Two blocks are connected by a thin string. The pulley is massless and frictionless. Friction between the 20.0 N block and the table causes the blocks to move at a constant speed. The 20.0 N block moves .750 m to the right and the 12.0 N block moves .750 m downward.

1) How much total work is done on the 12.0 N block? 2)How much work is done by gravity on the 12.0 N bock? 3)How much work does friction do on the 20.0 N block? 4) How much work is done by the tension force on the 20.0 N block?

Solution

Work Done = Force * Displacement in direction of Force.

On 12 N block,
Work done by gravity = change in potential energy of the block
= 12 * 0.75
= 90 J

Since change in kinetic energy of the block = 0, so according to work-energy theorem which states,
Work done by all forces on body = Change in kinetic energy of body,

Work done by tension + work done by gravity = change in kinetic energy of the block = 0
=> Work done by tension = - work done by gravity
=> Work done by tension = - 90 J

On 20 N block,
Work done by gravity = Displacement in direction of gravity * Force = 0 J
Work done by tension = 12 * 0.75 = 90 J