3. A 50 kg sled is pulled at a constant speed by a 70 N force. a) What is the force of friction? How do you know?
b) What is the coefficient of friction?
c) How much force is required to pull the sled with a 20 kg box on it?

conservation of mass

mass before something happens = mass afterwards

the best answer for these questions would be:

1.            c. is smaller

2.            d) concrete operational

3.            b) interaction with the environment – the children interact with their environment can them learn more.

4.            a) parents who reason openly with children can limit a child’s cognitive ability.