3.1 Forces and motion [Mastery check] 2

What is needed for two forces to be balanced?

(Can choose more than one choice.)

• Two forces must be the same size.

• Two forces must be different sizes.

• Two forces must be in the same direction.

• Two forces must be in opposite directions.

A box sits on the ground. The box is not moving.

• There are no forces acting on the box.

• There are balanced forces acting on the box.

• There is an unbalanced force acting on the box.

Which of these can happen because of unbalanced forces?

Can choose more than one​

• A boat will slow down
• A football will change direction
• A car will move at a constant speed
• A book will not move on a desk

The diagram shows the forces on a car which is started to move forward.

The unbalanced forces are ​..........................................

• weight
• contact force
• driving force
• friction

The helicopter begins to move upward when the upward force produced by its rotors is ​ (a)   than its weight.

• larger
• smaller

Hanna is cycling. Her legs provide a forward force of 150 N. Friction and air resistance give a combined force of 150 N. The resultant force is ​ (a)   and hence Hanna is moving at a ​ (b)   .​

• 0 N
• constant speed
• speed up
• slow down
• 300 N
• 150 N
• 300 N
• 150 N

Team A pull with a total force of 500 N and team B pull with a total force of 450 N. The resultant force is ​ (a)   . The rope starts to move towards Team ​ (b)   .

• 50 N
• A
• B
• 0 N
• 100 N

A car's engine provides a forward force on the car of 700 N. Friction and air resistance produce a combined backward force of 400 N. The resultant force is ​ (a)   . The car speed ​ (b)   .

• 300 N
• increases
• decreases
• remain the same
• 700 N
• 400 N

Calculate the resultant force on this box.

The resultant force is ​ (a)   .

The box is ​ (b)   .

• 5 N
• moving to the left
• not moving
• moving to the right
• 20 N
• 25 N

Sofia is riding her bicycle. The driving force on the bicycle is balanced with the force of friction on the bicycle.

Label the names of the forces.

c

d

b

a

driving force

friction and air resistance

weight

contact force