forces

Question 1

the weight of a brick is equal to the normal reaction of the ground on the brick; explain why these 2 forces are not an example of newton’s third law of motion

Answer 1

both act on the brick; they are 2 different types of forces

Question 2

state the principle of moments

Answer 2

for a body in equilibrium, sum of clockwise moments = sum of anticlockwise moments

Question 3

a ball is rolled off a horizontal table; explain how its time of flight depends on its speed

Answer 3

flight time does not depend on speed; because distance of fall stays the same + velocity always starts horizontal

Question 4

a ball is rolled off a horizontal table; explain how its horizontal distance travelled before hitting the floor depends on its speed

Answer 4

d = vt; distance proportional to speed because fall time stays the same

Question 5

what is the torque of a couple

Answer 5

one of the forces x perpendicular distance between them

Question 6

why does speed not change during circular motion (despite there being a force)

Answer 6

force is perpendicular to velocity; so overall no work is done

Question 7

what is drag

Answer 7

friction force on an object moving through a fluid

Question 8

what is upthrust

Answer 8

weight of liquid displaced