topic 9

Question 1

wooden block with pulley, weight, wooden block and string.

explain how the forces keep the wooden block moving across the table at a constant horizontal velocity

Answer 1

tension is one of the horizontal forces acting on the wooden block. friction acts in the opposite direction to the tension between the table and the wooden block. the forces are equal and opposite so there are no resultant forces and the block moves at a constant horizontal velocity. the weight of the block downwards and the normal reaction are equal and opposite so the bock doesnt move up or down

Question 2

describe the relationship between the upward force and speed shown by graph

Answer 2

upward force increases with speed. relationship is non linear

Question 3

explain why it is easier to close door by pushing at point P than point Q

Answer 3

distance from hinges increased therefore smaller door needed

Question 4

in which of these forces acting on a seesaw be in equilibrium?

A
B
C
D

Answer 4

B

Question 5

explain how the oil improves the efficiency of the bicycle

Answer 5

reduces amount of thermal energy transferred. extra useful energy is available and efficiency = useful energy by bicycle / total energy transferred by bicycle

Question 6

large gear - 48 teeth
small gear - 12 teeth
large gear turns 2 times each second

calculate amount of times the small gear turns each second

Answer 6

2 x 48 = turns x 12

8 turns per second

Question 7

rock weighs 1800N
persons can only produce a downwards force of 600N person cannot lift rock

explain using calculations why the person cannot lift the rock

Answer 7

moment = force x distance

moment of force from person = 600 x 0.5 = 300
moment of weight of rock = 1800 x 0.2 = 360
moment of force from person is less than the rock

Question 8

which force will make the rod rotate about the axle?

A) P
B) Q
C) R
D) S

Answer 8

B) Q