Answer:
D. a person pulling a sled.
Explanation:
contact force only occurs when something directly comes in contact with another object.
a. is wrong because that is called magnetic force.
b. gravitational force
c. is an electrical force
Answer:
a

b

Explanation:
From the question we are told that
The mass of the rock is 
The length of the small object from the rock is 
The length of the small object from the branch 
An image representing this lever set-up is shown on the first uploaded image
Here the small object acts as a fulcrum
The force exerted by the weight of the rock is mathematically evaluated as

substituting values


So at equilibrium the sum of the moment about the fulcrum is mathematically represented as

Here
is very small so
and 
Hence

=> 
substituting values


The mechanical advantage is mathematically evaluated as

substituting values


The answer is C voltmeter
Answer:
Drug abuse is best defined as the nonmedical or improper use of a drug that can interfere with a healthy life.
For example, a person that is addicted to cocaine will use it everyday, and will develope agressive behavior, anxiety, sleep disorder, paranoia etc.
This person could get addicted at the point of comiting a robbery, killing and much more.
Answer:
Object B has greater density
desity A=20/10=2 g cm^-3 . density B=50/10=5 g cm^-3
the object that has greater mass has the greater density because the volume of the those two objects are same