Problem 1 / Lecture 5 (Work)

A block of mass is pushed a distance along with a frictionless horizontal table by a constant applied force of magnitude directed at an angle below the horizontal. Determine the work done by (a) the applied force, (b) the normal force exerted by the table, (c) the force of gravity, and (d) the net force on the block.

Answer: (a) 31.9 J (b) 0 (c) 0 (d) 31.9 J

Problem 2 / Lecture 5 (Kinetic Energy and Work-Energy Theorem)

An outfielder throws a 0.150-kg baseball at a speed of 40.0 m/s and an initial angle of. What is the kinetic energy of the ball at the highest point of its motion?

Answer: 90 J

Problem 3 / Lecture 5 (Kinetic Energy and Work-Energy Theorem)

A 2000-kg car moves down a level highway under the actions of two forces: a 1000-N forward force exerted on the drive wheels by the road and a 950-N resistive force. Use the work-energy theorem to find the speed of the car after it has moved a distance of 20 m, assuming that it starts from rest.

Answer: 1.0 m/s

Problem 4 / Lecture 5 (Gravitational Potential Energy)

A child is in a swing that is attached to ropes 1.75 m long. Find the gravitational potential energy associated with the child relative to her lowest position when (a) the ropes are horizontal, (b) the ropes make a angle with the vertical and (c) the child is at the bottom of the circular arc.

Answer: (a) 613 J (b) 82.1 J (c) 0

Problem 5 / Lecture 5 (Energy Conservation)

A child and a sled with a combined mass of 50.0-kg slide down a frictionless slope. If the sled starts from rest and has a speed of 3.00 m/s at the bottom, what is the height of the hill?

Answer: 0.459 m