Nuclear decay revision

Acceleration and Force Newton's Laws

Force calculations

Force

1.             A car of mass 1000 kg travelling at 10 m/s stops in 4 s        

Calculate     a) the average deceleration.

                                    b) the braking force.

2.         An aeroplane accelerates uniformly from rest (0 m/s) to 200 m/s in 40 s.

            What force does it exert on a pilot whose mass is 90 kg?

3.         The valve of a cylinder on an engine containing 12 kg of compressed gas is opened       and the cylinder empties in 1min 40 sec. If the gas leaves its chamber at 25 m/s       find.

            a)         the acceleration of the gas.

            b)         the force exerted on the chamber.

4.         A bullet of mass 20 g travelling with a velocity of 300 m/s hits an earth bank and is          brought to rest in 0.2 s.

            Find      a) the deceleration of the bullet.

                                     b) the force it exerts on the earth bank.

5.         A car hits a wall and decelerates at 40 m/s².  It exerts a force of 20 000 N on the wall.  What is the mass of the car?

6.         A stone of mass 0.5 kg falls into a sandpit exerting a force of 5N.  What is its     acceleration?

7.         A car of mass 750 kg stops uniformly in 5s.  If its initial velocity was 15 m/s calculate      the braking force.

Velocity time graphs

Velocity and Vt Time graphs

Einstein

Revision Power

Answers to worksheets

Power is the rate of doing work. Power is measured in watts (W). An object has a higher power if it does more work in a certain time, or if it takes less time to do a certain amount of work.

2

Person	Force (N)	Distance moved (m)	Work done (J)
Alice	50	3	150
Bernard	10	10	100
Courtney	200	1	200
Dionne	500	0.3	150
Edward	75	2	150

3      Lowest power        Bernard (10 W)

                                      Alice (15 W)

                                      Courtney (20 W)

                                      Edward (25 W)

                                      Dionne (30 W)

1      70 x 9.8 x 5 = 3430 J

2      3430/7 = 490 W

3      The work done on each flight of stairs is the same as the one before.

4      The time taken to climb each flight of stairs is longer than the one before.

5      (Exact figures may vary slightly depending on whether pupils calculate each time separately from work/power or calculate the increase from the previous time directly.)

Flight of stairs	Work done in climbing flight (J)	Power (W) (to 1 d.p.)	Time to climb flight (s) (to 1 d.p.)
1	3430	490.0	7.0
2	3430	465.5	7.4
3	3430	442.2	7.8
4	3430	420.1	8.2
5	3430	399.1	8.6
6	3430	379.2	9.0
7	3430	360.2	9.5
8	3430	342.2	10.0

6      Work = 3430 x 8 = 27 440 J, time = 67.5 s, Power = 406.5 W (to 1 d.p.)

Work and energy revision

Answers to worksheet

http://physicstwyford.blogspot.com/2010/09/y12-homework-on-gpe-and-ke.html

Nuclear Fission