Energy – Class Question
1.
A spring–loaded toy dart gun is used to shoot a dart straight up in the air, and the dart reached a
maximum height of 24 m . The same dart is shot straight up a second time from the same gun, but
this time the spring is compressed only half as far before firing. How far up does the dart go this
time (neglecting friction and assuming an ideal spring)?
2.
I am mowing the grass in my backyard. I push the lawn mower around the outside edge of my yard.
The grass is uniformly long and so the force, F , required to push the mower along any side is the
same. The yard is essentially a square of side l . How much work do I do on the lawn mover as I
move it completely around the perimeter?
3.
A puck on the end of a string is swinging in a circle at a constant speed on a horizontal frictionless
air table. A tension T in the string holds the puck on its circular trajectory of radius r . How much
work is done on the puck by the tension in the string during one half revolutions?
4.
A simple pendulum swings from its highest position to its lowest position. The forces acting on the
suspended mass are gravity, the tension in the supporting cord, and air drag. What is the sign of the
work done by each of the forces?
5.
A 1.0 kg block slides down a 5.0 m long inclined plane. How much work is down on the block by
the normal force?
6.
A 1.0 kg block slides down a 5.0 m long inclined plane. How much work is down on the block by
the force of gravity?
7.
A boy lifts a stone of mass m through a vertical distance ∆ y .What is the net work done on the
stone between the initial and final positions?
8.
Two ants carry equal loads of food to the top of an ant hill. The first one carries its load on the
shorter (steeper) side of the hill while the second one takes the longer (less steep) side. If each ant
crawls at a constant speed, which ant does more work on the food?
9.
Block A slides down a frictionless plane inclined at an angle φ . Block B slides down a second
frictionless plane which has the same vertical height, but which is inclined at an angle of 2 φ . How
do the speeds of the blocks compare at the bottom of the inclined?
10. A 1.0 kg block starts from rest and slides down a 3.0 m high and 5.0 m long incline. A kinetic
frictional force of 2.0 N acts on the block as it slides. What is the kinetic energy of the block when
it reaches the bottom of the ramp?
11. A stone is lunched upward into the air. In addition to the force of gravity, the stone is subject to a
frictional force due to air resistance. How does the time that the stone takes to go up compare to the
time that it takes to come down?