8.2- USING F=ma

Question 1

What happens when an object is acted on by two unequal forces acting in opposite directions?

Answer 1

object accelerates in direction of larger force

Question 2

What is the equation of the resultant force when an object is acted on by two unequal forces acting in opposite directions?

Answer 2

resultant force, F1 - F2 = ma

Question 3

When towing a car, what is the resultant force on the car?

Answer 3

resultant force = F - T = Ma

Question 4

What is the force on the trailer due to?

Answer 4

tension T in tow bar pulling it forwards

Question 5

What is the equation for the tension in the tow bar (towing a trailer)?

Answer 5

T = ma

Question 6

What does combining the two equations for towing a trailer give?

Answer 6

F = Ma + ma = (M + m)a

Question 7

What is the equation for the thrust of the rocket?

Answer 7

T = mg + ma

T- thrust
m- mass
a- acceleration

Question 8

What must the rocket thrust overcome to take off?

Answer 8

overcome weight of rocket

Question 9

Lift problems equation

Answer 9

T - mg = ma

T- tension in lift cable
m- total mass of lift
a- acceleration

Question 10

Equation when lift is moving at constant velocity?

Answer 10

a=0

T =mg

Question 11

Equation for when lift moving up + accelerating?

Answer 11

then a>0,

T = mg + ma > mg

Question 12

Equation for when lift moving up + decelerating

Answer 12

then a<0,

T = mg + ma < mg

Question 13

Equation for when lift moving down + accelerating?

Answer 13

then a<0,
T = mg + ma < mg
(velocity + acceleration downwards so negative)

Question 14

Equation for when lift moving down + decelarating?

Answer 14

then a>0,
T = mg + ma > mg
(velocity downwards + acceleration upwards so positive)

Question 15

When is the tension in the cable less than the weight? (2)

Answer 15

if:
lift moving up + decelerating (velocity > 0 + acceleration < 0)

lift moving down + accelerating (velocity > 0 + acceleration > 0)

Question 16

Pulley problems: equation for result force on mass M? (where M>m)

Answer 16

Mg - T = Ma

Question 17

Pulley problems: equation for result force on mass m? (where M>m)

Answer 17

T - mg = ma

Question 18

What does adding the two equations for the pully problems give?

Answer 18

Mg - mg = (M + m)a

Question 19

Sliding down a slope: what is the equation for the component of the block’s weight down the slope?

Answer 19

= mgsinθ

Question 20

Sliding down a slope: what is the resultant force on the block if the friction on the block is = F0

Answer 20

= mgsinθ - F0

Question 21

What is the overall equation for ‘sliding down a slope’?

Answer 21

mgsinθ - F0 = ma

Question 22

Equation for acceleration when a vehicle is on a downhill slope of a constant gradient?

Answer 22

Fe + mgsinθ - F0 = ma

Fe- engine force
F0- combined sum of air resistance + braking force