Twenty Questions

Dynamics

Twenty Questions

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

1. What is the unbalanced force?

• 15N – 7N• 8N right

15N7N

2. What force always acts in the opposite direction to motion?

• Friction.

3. Complete the table.

Planet Gravity (N/kg)

Mass of object (kg)

Weight of object (N)

Earth 10

Mars 4

9.8

10

98

40

4. Why does ½ mv2 = mgh?

• Energy is always conserved.

5. What is Kinetic energy?

• The energy an object possesses due to it’s motion.

• The work done against gravity in raising an object.

6.What is Gravitational potential energy?

7. What formula denotes Electrical power?

• P = E/t

8. What are the units of energy?

• Joules.

9. Calculate the acceleration of the rocket as it takes off.

• Fun =ma

• a =Fun/m

• a =(21000000-7000000) (7000000/9.8)

• a = 19.6ms-2

7000kN

21000kN

10. A ball rolls off a cliff, travelling at 3m/s. It hits the water below 5s later.

• 3m/s

What is it’s final horizontal speed?

11. A ball rolls off a cliff, travelling at 3m/s. It hits the water below 5s later.

• d = vt

• d = 3 x 5

• d = 15m

How far does the ball land from the base of the cliff?

12. Give one situation in which friction is increased.

• i) applying the brakes of a car.• ii) opening a parachute.• iii) wearing rubber soled shoes for rock climbing.

13. A ball rolls off a cliff, travelling at 3m/s. It hits the water below 5s later.

• v = u +at • v = 0 + 9.8(5) • v = 49ms-1

What is it’s final vertical velocity?

14. What is Newton’s first law of motion?

• When balanced forces (or no forces at all) act on an object it remains at rest or continue to move at a steady speed in a straight line unless acted upon by an unbalanced force.

15. A 100kg man takes 10s to accelerate to 20m/s from rest. What force does he exert to do this?

• F = ma = 100(2) = 200N

• a =(v-u) = (20-0) = 2ms-2

t 10

16. What is Newton’s second law of motion?

• Fun = ma

17. A tram takes 25s to gain 10kJ of Potential energy. How powerful is the tram’s motor?

• E =Pt• P = E/t • P = 10000/25 • P = 400W

18. Give one situation in which friction is decreased.

• i) making racing cars streamlined.• ii) oiling moving parts in a car engine.• iii) using an air cushion on an ‘air hockey’ table.

19. State the principle of conservation of energy.

• During any energy transformation the total amount of energy remains the same.

20. What does the formula Ew = Fd represent?

The work done in moving an object.