Resultant Forces

What is the name of the force from the water in this picture?

• Upthrust

• Lift

• Air resistance

• Weight

Answer explanation

Upthrust is the force caused by a fluid like water or gas. 

In an accelerating car, which force is unbalanced? 

• Weight

• Thrust

• Normal Reaction Force

• Air resistance

Answer explanation

The unbalanced thrust means a change in the forward velocity. 

The name for the overall force acting on an object is ______

• The balance force

• The strongest force

• The weight force

• The resultant force

Answer explanation

The resultant force is the force you get when you put together the effect of all of the forces acting on an object. 

When do you add forces together? 

• When they are in the same direction

• When one is up and one is sideways

• When there is more than one

• When they are in opposite directions

What is the size and direction of the normal reaction force which would balance a 50N dog? 

• 5 kg upwards

• 50 N upwards

• 50 N downwards

• It is already balanced

Answer explanation

A force which balances is the same size, in the opposite direction. The force of the dog is downwards so the reaction force 50 N upwards.

For a boat to float, the upthrust and the weight must ________ 

• be the same size in opposite directions

• both be upwards

• be identical

• add up to cause it to float

Answer explanation

They have to balance so give the same force in opposite direction.

What statement is true if an object is accelerating? 

• There is no air resistance

• It has thrust

• Forces are unbalanced

• Friction is useful in this case

Answer explanation

An object will only change velocity when forces are unbalanced.