Mechanics | Relativity Answers

Three boxes of equal dimensions (20 cm x 30cm x 50 cm), containing material which density 6.8x10-2 g/cm3 are to be stored for winter. What is the least amount of pressure that can be exerted by the blocks?
a) 1999.2 g/cm.s2
b) 40 Pa
c) 666 Pa
d) 4000 g/cm.s2
e) 333 Pa

A person travels following displacement:
3m North
4m West
5m south to east 45 degree
Find its resultant displacement if sin45=cos45=0.7

When a bat walks over ground searching for insects (its prey), it is usually guided more by hearing an insect than by seeing it because a bats vision is poor and they search at night. However some types of bats can detect and capture an insect, such as a moth, when both are in fight. Although the bat flies quickly, it can home in on an insect and nab it. How does the bat detect not only the presence of the insect but also its direction and speed of flight?
Why do bats have a better time nabbing flying moths near a mercury vapor lamp (commonly used as a street lamp) than over an open field? Why does the advantage disappear if the lamp is a sodium vapor lamp?
Bats can roost in deep, dark caves flying in and out to forage for food. In the complete darkness of a twisting passage of a cave they do not fly into the walls. How do they do that?

A head-on collision is the most dangerous type of car collision. Surprisingly the data collected about head-on collisions suggest that the risk (or probability) of fatality to a driver is less if that driver has a passenger in the car. Why is that?

Question 5
A “T” section consists of a vertical rectangle (Element 1) of width 8 mm and height 110 mm, and a horizontal rectangle (Element 2) of width 60 mm and height 10 mm.
Find the distance y from the horizontal bottom edge of the vertical
rectangle to the centroid of the “T” section, and the second moment of area, Ixx, of the “T” section about the centroidal horizontal axis.

An object moving at speed of 20ms-1 loses its speed by 3ms-2 . How does it travel before it stops?

A rocket climbs vertically and is powered in such a way that it has constant acceleration a. It reaches a height of 1km with a velocity of 100m/s. What is the value of a? How long does the rocket take to reach this 1km height?

A stone is dropped from rest into a well. It is observed to hit the water after 2s. Find the distance down to the water surface. How fast must the stone be thrown downward in order to hit the surface after only 1s? What are the impact velocities in the two cases?

Taking off from a point on the equator in the late afternoon and flying due west, passengers on the concorde supersonic airliner see the sun set and then rise again ahead of them. Estimate concorde’s minimum speed. (Earth’s radius=6400km)

A ball is thrown vertically upwards with initial speed 10m/s^-1 from the edge of a roof of height H= 20m. How long does it take for the ball to hit the ground? At what velocity does it hit the ground?