Question

Ocean waves travel in to the beach at an average velocity of 2.5 m/s
If these waves come in 4 seconds apart, what is the average distance between the wave peaks, considering the formula V=d/t
A) 0.625 m
B) 1.6 m
C) 5.0 m
D) 10.0 m

The wattage of speaker describes the rate at which energy is converted from electrical energy to sound energy. This is the description of which of these?
A) Energy
B) Power
C) Transformation
D) Work

A bodybuilder lifts a certain weight up and down. If the body builder does it in less time, which of these statements is most accurate?
A) The body builder uses both the same energy and power.
B) The body builder uses both more energy and more power.
C) The body builder uses the same energy and but more power.
D) The body builder uses the same power and but more energy.

Students in a physical education class practiced rope climbing. Students gripped a rope that hung from the ceiling and lifted themselves up the rope using only their arms. What must be measured to determine the power output of the climbers?
A) tension on the rope and the final height
B) body mass, final height, and the tension on the rope
C) tension on the rope and the time required to complete the climb
D) body mass, final height, and the time required to complete the climb

Answer 1

1) D) 10.0 m

To find the average distance between the wave peaks, we can use the formula:

$v=\frac{d}{t}$

where in this case:

v = 2.5 m/s is the average velocity

d = ? is the average distance

t = 4 s is the time between two wave peaks

Re-arranging the equation, we find

$d=vt=(2.5 m/s)(4 s)=10.0 m$

2) B) Power

This is exactly the definition of power. In fact, power is defined as the ratio between the amount of work done / of energy used, and the time taken for this conversion to occur:

$P=\frac{W}{t}$

where

W is the amount of work done / of energy used

t is the time taken

3) C) The body builder uses the same energy and but more power.

The energy used by the body builder does not change: in fact, it is only related to the height at which he lift the weight. The work done to lift the weight, of mass m, up to a height of h, is given by

$W=mgh$

where g is the gravitational acceleration. So, this quantity does not change. Instead, the power changes, because the time the body builder takes to lift the weight up has decreased, and the power depends on the time as we know from the formula:

$P=\frac{W}{t}$

so, since t has decreased, P has increased.

4) D) body mass, final height, and the time required to complete the climb

The power output is given by:

$P=\frac{W}{t}=\frac{mgh}{t}$

where:

m is the body mass

g is the gravitational acceleration

h is the final height

t is the time required to complete the climb

Therefore, we see that correct choice is D.