Physics Answers

1. A refrigerator and a rice cooker are connected in parallel to a 220 V line. The current in the refrigerator is 10 A and in the rice cooker is 4 A. Find the following;

(a) the resistance of each device

(b) the total resistance

(c) the current flowing in the line

a proton moving horizontally at 3.5x10^4 m/s enters a uniform magnetic field of 0.075 t directed upward at 30°with the horizontal. find the magnitude of the magnetic force acting on the proton

7. Using the formula at the beginning of this lesson, calculate the wavelength of a signal from KPhET 98.7. Remember that FM stations transmit in the Megahertz range. This means that KPhET is transmitting a frequency of 9.87 x107 hz. What is the wavelength of the signal from this radio station?

8. My favorite radio station is NPR, which transmits a signal that is has a wavelength of 3.38 m. What is the frequency of this signal? Remember, light speed is 3 x108 m/s.

9. AM 630 is where I listen to sports. The frequency is 630 khz (or 630,000 hz). What is the wavelength?

10. Pick your favorite radio station, or one your friends listen to. What is its frequency and wavelength?

Abbey and Mia are in the basement playing pool. On Abbey's recent shot, the cue ball was moving east at 82 cm/s when it struck the slower 5-ball moving in the same direction at 24 cm/s. The 5-ball immediately speeds up to 52 cm/s. Determine the post-collision speed of the cue ball in cm/s.

Bailey is on the tenth frame of her recent bowling competition and she needs to pick up the last pin for a spare and the first place trophy. She rolls the 7.39 kg ball down the lane and it hits the 1.41 kg pin head on. The ball was moving at 7.9 m/s before the collision. The pin went flying forward at 1.7 m/s. Determine the post-collision speed of the ball.

An 108.0 kg boy and a 61.1 kg girl, both wearing skates face each other at rest on a skating rink. The boy and girl push each other, sending her eastward with a speed of 3.09 m/s. Determine the final velocity of the boy. Neglect friction.

A bicycle has a momentum of 24 kg m/s. What momentum would the bicycle have if it had…

… twice the mass and was moving at the same speed?

Answer 1

… the same mass and was moving with one-half the speed?

Answer 2

… three times the mass and was moving with twice the speed?

Answer 3

… one-half the mass and was moving with twice the speed?

Answer 4

… the same mass and was moving with twice the speed?

Answer 5

… three times the mass and was moving with one-half the speed?

When the blender is empty and running at high speed, how much time is required for a blade to turn by 90 degrees

A child throws a 0.50 kg snowball at his friend at 12.0 m/s but the snowball lands on the ground in front of his friend.

The snowball is 1.3 m above the ground when it leaves the child’s hand.

(a) What is the (i) kinetic energy & (ii) potential energy of the snowball at the time of release?

(b) What is the total energy of the snowball (i) at the time of release & (ii) just before it hits the ground?

(c) What is the snowball’s kinetic energy just before it hits the ground in front of his friend?

(d) How fast is the snowball moving just before it hits the ground in front of his friend?

A toboggan carrying two children (total mass = 85 kg) reaches its maximum speed at the bottom of a hill, and then glides to a stop in 21 m along a horizontal surface.The coefficient of kinetic friction between the toboggan and the snowy surface is 0.11.

(a) Draw a FBD of the toboggan as it slows down, and calculate the magnitude of ALL the forces in the diagram.

(b) Calculate the acceleration of the toboggan.

(c) Calculate the work done on the toboggan by the friction on the snowy surface.Should the work be positive or negative?Explain.