Other Physics Answers

A car's bumper is designed to withstand a 5.04-km/h (1.4-m/s) collision with an immovable object without damage to the body of the car. The bumper cushions the shock by absorbing the force over a distance. Calculate the magnitude of the average force on a bumper that collapses 0.255 m while bringing a 820-kg car to rest from an initial speed of 1.4 m/s. 

Force is a vector quantity and thus has both a magnitude and a direction.

A vector can be represented graphically by a line drawn to scale in the

direction of the line of action of the force. To distinguish between vector

and scalar quantities, various ways are used. Identify and explain three

of these ways.

1. Consider a person sitting nude on a beach in Florida. On a sunny day, visible radiation energy from the sun is absorbed by the person at a rate of 30 kcal/h or 34.9 W. The air temperature is a warm 30 ℃ and the individual’s skin temperature is 32 ℃. The effective body surface exposed to the sun is 0.9 m2.

(4 pts.) Find the net energy gain or loss from thermal radiation each hour.

(4 pts.) If there is a 4 m/s breeze, find the energy lost by convection each hour.

(4 pts.) If the individual’s metabolic rate is 80 kcal/h (93.0 W) and breathing accounts for a loss of 10 kcal/h (11.6 W), how much additional heat must be lost by evaporation to keep the body core temperature constant?

(3 pts.) How would you suggest that he loses this energy? Explain your answer clearly and convincingly.

During a very quick stop, a car decelerates at 7.00 m/s² .

a). What is the angular acceleration of its 0.280 m radius tires, assuming they do not slip on the pavement?

b). How many revolutions do the tires make before coming to rest, given their initial velocity is 95.0 rad/s?

c). How long does the car take to stop completely?

d). What distance does the car travel in this time?

e). What was the car's initial velocity?

f). Do the values obtained seem reasonable, considering that this stop happens very quickly?

A crate of eggs is located in the middle of the flat bed of a pickup truck as the truck negotiates an unbanked curve in the road. The curve may be regarded as an arc of a circle of radius r = 35.0m. If the coefficient of static friction between crate and truck is 0.600, how fast can the truck be moving without the crate sliding?

Two blocks of masses M and 3M are placed on a horizontal, frictionless surface. A light spring is attached to one of them, and the blocks are pushed together with the spring between them. A cord initially holding the blocks together is burned; after this, the block of mass 3M moves to the right with a speed of 2.00 m/s.

a). What is the speed of the block of mass M?

b). Find the original elastic potential energy in the spring if M = 0.350kg.

A 300kg particle has a velocity of (3.00i - 4.00j) m/s.

a). Find it's x and y components of momentum.

b). Find the magnitude and direction of its momentum.

A small rock with mass 0.20kg is released from rest at point A, which is at the top edge of a large hermisperical bowl with radius, r = 0.50m. Assume that the size of the rock is small compared to the radius, so that the rock can be treated as a particle, and assume that the rock slides rather than roll. The work done by friction on the rock when it moves from point A to point B at the bottom of the bowl has a magnitude of 0.22J.

a). Between points A to point B, how much work is done on the rock by;

i). The normal force and ii). The gravity?

b). What is the speed of the rock as it reaches point B?

c). Of the three forces acting on the rock as it slides down the bowl, which, if any, are constant and which are not? Explain.

d). Just as the rock reaches point B, what is the normal force on it due to the bottom of the bowl?

A bus is going up a hill inclined at

30o

 and is accelerating at 5m/s2

. A pendulum is attached to the roof of the bus. What angle does

the pendulum make with the roof of the bus?

Solve the following problems.

1) Suppose that a resistor is connected to a 12.0-V battery through the simple circuit

shown in the diagram. Using Ohm’s Law, calculate the resistance of the resistor if

the current measured by the ammeter is:

a) 0.0364 A

b) 2.00 A

c) 0.00444 A

d) 0.240 A

e) 0.000120 A

2) In each case, calculate the resistivity of the material used for the resistor if the

resistor has a length of 0.00750 m and cross-sectional area of 0.00842 m2.