Question

1. increasing an objects height above the ground increases its:

a. kinetic energy
b. chemical energy
c. elastic energy
d. gravitational potential energy

1. a light bulb converts electrical energy into which two main forms of energy?

a. nuclear and chemical
b. heat and light
c. potential and kinetic
d. sound and mechanical

1. which of the following situations involves no work being done on the object?

a. carrying a backpack while walking across a flat floor
b. pushing a cart up a ramp
c. lifting a book onto a shelf
d. pulling a sled through snow

1. two runners each do the same amount of work, but one finishes faster. which statement is true?

a. they have the same power output
b. the faster runner has greater power
c. the slower runner has greater power
d. power is not related to time

1. a bicyclist at the top of a hill begins to coast down. as the rider speeds up, which statement best describes the energy change?

a. kinetic energy decreases while potential energy increases
b. kinetic energy and potential energy both increase
c. potential energy decreases while kinetic energy increases
d. both forms of energy remain constant

Explanation:

• Question 26: Gravitational potential energy formula is \(U = mgh\) (where \(m\) is mass, \(g\) is acceleration due to gravity, \(h\) is height). As \(h\) increases, \(U\) increases. Kinetic energy (\(K=\frac{1}{2}mv^{2}\)) depends on speed, chemical energy is stored in chemical bonds, and elastic energy (\(U=\frac{1}{2}kx^{2}\), \(k\) - spring constant, \(x\) - displacement) is for deformed elastic objects.
• Question 27: A light - bulb works by passing an electric current. Due to resistance in the filament, it heats up (heat energy) and emits light (light energy). Nuclear energy is from nuclear reactions, chemical energy is stored in substances, potential and kinetic are mechanical energy forms, and sound and mechanical are not the main energy outputs of a light - bulb.
• Question 28: Work formula is \(W = F\times d\times\cos\theta\) (where \(F\) is force, \(d\) is displacement, \(\theta\) is the angle between force and displacement). When carrying a backpack while walking on a flat floor, the force (upward to hold the backpack) and displacement (horizontal) are perpendicular (\(\cos90^{\circ}=0\)), so \(W = 0\). Pushing a cart up a ramp (\(F\) and \(d\) in the same general direction), lifting a book (\(F\) and \(d\) in the same direction), and pulling a sled (\(F\) and \(d\) have a non - zero component of force in the direction of displacement) all involve work.
• Question 29: Power formula is \(P=\frac{W}{t}\) (where \(W\) is work, \(t\) is time). If \(W\) is the same (\(W_1 = W_2\)), and \(t_1\lt t_2\) (faster runner has smaller \(t\)), then \(P_1=\frac{W}{t_1}\gt P_2=\frac{W}{t_2}\).
• Question 30: At the top of the hill, the bicyclist has gravitational potential energy (\(U = mgh\)) and some initial kinetic energy (assuming starts from rest, initial \(K\) is very small). As they coast down, \(h\) decreases (so \(U\) decreases) and speed (\(v\)) increases (so \(K=\frac{1}{2}mv^{2}\) increases) due to the conversion of potential energy to kinetic energy (neglecting friction for simplicity).

Answer:

1. d. Gravitational potential energy
2. b. Heat and light
3. a. Carrying a backpack while walking across a flat floor
4. b. The faster runner has greater power
5. c. Potential energy decreases while kinetic energy increases