Physics (Essay) Paper 2 WASSCE (PC 2ND), 2020

Question 8

 

(a)(i) Define work.

(ii) A force F acts on a body of mass m, causing the body to accelerate at a ms-2 The
body travels through a distance s m in time t s in the direction of the force. Show that the work done is equal to change in the kinetic energy of the body.

 

(b)(i) Define kinetic friction.

(ii) State two factors which affect kinetic friction

 

(c)The diagram below illustrates three similar blocks, labeled A, B, C, each of mass 3 kg and are joined by strings. They are pulled along a horizontal floor by means of the string at A with an acceleration of 2 ms-2. The strings are under tension TC, TB and TA.

kinetic

If the coefficient of kinetic friction between the surfaces is 0.3, calculate;
(i) TC;
(ii)  TB;
(iii)  TA.

 

Observation

 

(a)    (i)         Definition of work
The product of force and distance moved in the direction of the force         
                    
                     (ii)      

                                           kinetic theory

 

 

         (b)        (i)         Definition of kinetic friction
The force that opposes motion between two surfaces in contact and in relative motion.     

                     (ii)        Factors that affect kinetic friction
-           nature of the surfaces in contact        
-           weight of object/normal reaction       


(c)        Calculation of
Given mC = mB = mA = 3 kg
(i)         TC

TC – mmcg = mca                    
TC – 0.3 x 3 x 10 = 3 x 2        
TC – 9 = 6
TC = 15 N                               


(ii)        TB

                                 TB – TC – mmBg = mBa                       
TB – 15 – 0.3 x 3 x 10 = 3 x 2            
TB – 15 – 9 = 6
TB = 30 N                                                       

(iii)       TA

TA – TB – mmAg = mAa                                  
TA – 30 – 0.3 x 3 x 10 = 3 x 2           
TA – 30 – 9 = 6

                                    TA = 45 N