Mechanics | Relativity Answers

A cannon shell is fired straight up from the ground at an initial speed of 225 m/s. After how much time is the shell at a height of 6.20 × 102 m above the ground and moving downward?

a) A driver was speeding with 40 m/s in his 1800 kg car when he notices a police car with a radar and slows down to a legal speed of 19 m/s. What is the change of the kinetic energy of the car? What is the amount of work done on the car during the deceleration?

b) A repairman of mass 80 kg climbed a 10 m vertical latter to reach the roof of a building in 12 seconds. What is the power developed by the man against gravity?

A hockey puck lies still on ice. Another hockey puck is hit and is on course of collision with it with an initial velocity of +v. The pucks have the same mass and have glue around their edges. Neglect friction with ice. Predict the velocity that the puck which was initially at rest will have after collision, knowing that the pucks will stick together:

a) –v

b) +v

c) –v/2

d) +v/2

A squash ball hits a wall with an initial speed of u and it rebounds in the opposite direction with speed v. Knowing that some energy has been lost through heat in the collision so that v < u and that the duration of the collision is t, find the magnitude of the average force exerted by the wall on the ball.

a) F = m(u+v)/t

b) f = m(u-v)/t

c) F = 0

d) F = m(2v-u)/t

A box rests on a surface that is lifted by one end to create a larger and larger angle with the horizontal. When the surface reaches an angle of exactly 30 degrees with the horizontal, the box begins to slide down. What is the coefficient of static friction?

a)  μs = 1/√ 3

b)  μs = 2/√ 3

c)  μs = √ 3

d)  μs = 0.5

Calculations:

1. Suppose a large rock is ejected from a volcano with a speed of 25m/s and at an angle of 35*

the horizontal. If the rock strikes the side of the volcano at an altitude 20m lower than the star

point.

(a) Calculate the time it takes the rock to reach the starting point.

(b) What are the magnitude and direction of the rock's velocity at impact?

A sound wave of frequency 300 Hz travels with speed 340ms-1 along

the negative x-direction. Each point of the medium moves up and down through a

total distance of 5.0 mm. Determine the necessary parameters to represent the

wave mathematically.

At the surface of Jupiter’s moon Io the acceleration due to gravity is g=1.81 m/s2 . A watermelon weighs 44.0 N at the surface of the earth. a) What is the mass on the earth’s surface? b) What are its mass and weight on the surface of Io? 

QUESTION 1

A wave out in the deep ocean has an amplitude of 1.51 m, a wavelength of 212 m and a period of 14.3 s

What is the speed of such a wave? (in ms-1 to 3 s.f)

2 pts) A light wave is initially polarized in the +y direction and has intensity 1.0 W/m^2. It encounters a polarizer whose axis is 60 degrees counterclockwise from the +x axis. After the wave has emerged from the polarizer, i.

In which direction does its electric field point?

A. +x

B. +y

C. +z

D. 30° counterclockwise from +x

E. 60° counterclockwise from +x

ii. What is its intensity?

A. 0.25 W/m2

B. 0.50 W/m2

C. 0.75 W/m2

D. 0.87 W/m2

E. 1.0 W/m2