It is given that the height of the tower is
The uncertainty the measurement of this height is
Drop time is measured as:
The uncertainty in measurement of time is:
Using the equation of motion: 
where, 
is the distance covered, 
is the initial velocity, 
is the acceleration and 
is the time.
(because canon ball is in free fall). we need to calculate the value of a=g.
The uncertainty in this value is given by:
Substitute the values:
The hotter an object is, the more infrared radiation it emits. Infrared radiation is a type of electromagnetic radiation, which involves waves rather than particles. This means that, unlike conduction and convection, radiation can even pass through the vacuum of space.
Crossed electric field lines indicate A) a field pointing in two directions
The normal force is always (underline, bold) is always perpendicular to the surface an object is sitting on. If the object is on an inclined plane, then the normal will not be vertical but it will be perpendicular to the angle of the incline.
The diagram below (left) shows a normal force (GH) that is not vertical, but it is perpendicular to the surface. The object on the right is the more usual normal a mass on a table top.
The vertical line on the right is the normal and it points up.
Then only the component of the force that's parallel to the displacement
is used to calculate the work. The component of force that's perpendicular
to the displacement doesn't move through any distance at all, so its contribution
to the total work is zero.
