A crate of books is to be put on a truck with the help of some planks sloping up at 36◦ . The mass of the crate is 80 kg, and th
e coefficient of sliding friction between it and the planks is 0.8. You and your friends push horizontally with a force F~ . The acceleration of gravity is 9.81 m/s 2 .
The attached diagram shows the motion of crate on a single line The forces acting on it have been resolved as shown in the attached figure.The kinetic friction opposes the motion.Now crate is moving with constant speed so the acceleration is constant.
Applying Newton's second law to determine the force F and also substituting the values for to eliminate normal force
F = ma
Now and components are zero
Horizontal and vertical forces are Force on crate, weight of crate and kinetic friction
therefore
>>> (1)
By putting the above equation in equation 1 we get F
Water temperatures are slow to heat up, It takes 4 times the energy to heat up water than to heat air. Water also "feels" colder because water is a more efficent medium than air to cool our body down.