Question

(f) In order to find the height of a bridge, a rock was dropped off the bridge and timed. If it took three seconds to hit the water, what is the height of the bridge? 2marks 4. (a) Determine the distance covered by a body in 4.0s if its initial velocity, u is 20 m/s and acceleration is 4.0 m/s2. (4 marks) (b) state three effects of forces on objects (6 marks) (c) State two demerits of Friction and suggest two ways of reducing it. (4marks) (d) Explain three Clinical Applications of Gravity (6 marks

Answer 1

(f) time to drop off is ,t = 3 s

We know that ,

Distance coverd by an object dropped from hight is , H = ut + (1/2)gt^2

(H = height covered , u= initial velocity, t= time,

g= acceleration due to gravity =9.82 m/s^2)

Now , H = 0× t + (1/2)×9.81×3^2

= 0+ 44.145 = 44.145 m

So, the height of bridge is, H = 44.145 m

4.(a) initial velocity ,u = 20 m/s

Time taken , t= 4 s, acceleration, a= 4 m/s^2

Now, distance covered,

D = ut + (1/2)at^2

Or, D = 20×4 + (1/2)× 4×4^2

= 80 + 32 = 112 m

4.(b) Effects of force on an objects

1. To change the shape of objects

2. To move or stop the objects

3. To accelerate or deccelerate the objects

4.(c) Demerits of friction

1. Oppose the motion

2. Loss of energy as heat

Way for reducing friction are

1.POLISHING

2.LUBRICATION