Mechanical Energy

Try the following problems. Hover your mouse over each question to see the correct answer.

1) A sled with bricks has a total mass of 18.0 kg and is pulled at constant speed by a rope. The rope is inclined at 20.0o above the horizontal and the sled moves a distance of 20.0 m on a horizontal surface. The coefficient of kinetic friction between the sled and the surface is 0.500.

A. What is the tension of the rope? (Answer: 79.4 N)

B. How much work is done by the rope on the sled? (Answer: 1.49 kJ)

C. What is the mechanical energy lost due to friction? (Answer: -1.49 kJ)


2) A 70 kg base runner begins his slide into second base when moving at a speed of 4.0 m/s. The coefficient of friction between his clothes and Earth is 0.70. He slides so that his speed is zero just as he reaches the base.

A. How much mechanical energy is lost due to friction acting on the runner?

(Answer: -5.6 x 10^2)

B. How far does he slide?

(Answer: 1.2 m)


3) A 40 N toy is placed in a light swing that is attached to ropes 2.0 m long. Find the gravitational potential energy associated with the toy relative to its lowest position

A. when the ropes are horizontal

(Answer: 8.0 x 10^2 J)

B. when the ropes make a 30o angle with the vertical

(Answer: 1.1 x 10^2 J)

C. at the bottom of the circular arc

(Answer: 0)

4) A child and 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)

5) A gymnast swings on the high bar as shown below. Starting from rest directly over the bar, he swings around the bar while keeping his arms and legs outstretched. Treating the gymnast as though his entire mass were concentrated at a point 1.20 m from the bar, determine his speed as he passes under the bar at position XX.

Day 73 review5 image

Answer: (6.86 m/s)