Well, the 20 seconds gives us enough information to actually calculate the power she has on her feet :)
Well, the work is 500*15=7500J, that is 7.5 kJ or about 18 calories (1 cal is 418J?) The power is that 7.5 kJ divided by 20 seconds: 375W. That's... OK, I suppose...
Answer:
(a) 1, average velocity = -65.6 m/s
2, average velocity = -64.8 m/s
3, average velocity = -64.16 m/s
(b) The instantaneous velocity is -96 m/s
Explanation:
(a)
Average velocity is given by;

(1)

(2)

(3)

b. y = 235 - 16t²
The instantaneous velocity is given by;
v = dy /dt
dy / dt = -32t
when t = 3 s
v = -32(3)
v = -96 m/s
Answer:
(A) Equation will be 
(B) RMS value of voltage will be 0.530 volt
Explanation:
We have given peak to peak voltage of ac wave = 1.5 volt
Peak to peak voltage of ac wave is equal to 2 times of peak voltage
So 

Frequency of ac wave is given f = 3 kHz
So angular frequency
= 2×3.14×3000 = 18840 rad/sec
So expression of equation will be
( As phase difference is 0 )
Now we have to find the rms value of voltage
So rms voltage will be equal to 
The north arrow of the compasses will all point to the south since opposite poles attract. I have put an example picture below.
For the horse shoe magnet the magnetic field line will also go from north to south. I have put a picture of this below