Session 1: Kinematics Questions

Remedial Discussion Questions Linear Motion 1. When the velocity is constant, does the average over any time interval differ from the instantaneous velocity at any instant? 2. (a) Can an object have zero velocity and still be accelerating? (b) Can an object have a constant speed and still have a varying velocity? (c) Can an object have a constant velocity and still have varying speed? 3. Consider a ball thrown vertically up. Taking air resistance into account, would you expect the time during which the ball rises to be longer or shorter than the time during which it falls? 4. A driver had a reaction time of 0.5s, and the maximum deceleration of his car is 5 ms-2. What is the least distance in which he can bring the car to rest from a speed of 10 ms-1 ? What is the stopping distance of the car at a speed of 20 ms-1 ? Why is the second distance not twice the first one? 5. A boy standing at the edge of a cliff of 20 m above sea level, throws a stone straight up with a speed of 25 ms-1 . (a) How long does it take to reach its highest point? (b) How high does the ball rise above its release point? (c) How long will it take for the stone to reach a point 25 m above its release point? (d) Calculate the velocity of the stone when it hits the water surface. 6. A car accelerates uniformly from rest for t1s then its acceleration increases linearly with time for t2 s and finally its acceleration decreases linearly with time for t3 s. Sketch the graphs to show how the acceleration and velocity of the car vary with time. 7. A parachutist after bailing out falls 50 m without friction When the parachute opens, he decelerates downwards 2.0 ms-2. He reaches the ground with a speed of 3.0 ms-1. (a) How long is the parachutist in the air? (b) At what height did he bail out? 8. A body accelerates uniformly from rest along a straight line. Sketch a graph showing how the displacement of the body varies with time. How is the instantaneous velocity of a particle obtained from a graph of displacement against time? 9. A cricketer throws a ball vertically upwards and catches it 3.0 s later. Neglecting air resistance, find (a) the speed with which the ball leaves his hands (b) the maximum height to which it rises (c) Draw a sketch graph showing how the velocity of the ball depends on time during its flight. Mark on your graph the times at which

(i) the ball leaves the cricketer’s hands (ii) it comes to its maximum height (iii) it reaches his hands again (no need to calculate particular values for velocity) Non-linear motion (projectile motion) 1.

h

The stone as shown in the diagram is being thrown from the top of a cliff with the velocity of 15 ms-1 at 60˚ to the horizontal. Sketch the graphs to represent the variation with time of (i) VH, the horizontal component of the velocity (ii) Vv, the vertical component of the velocity of the stone. Ignore the air resistance. Find h, the maximum vertical height of the stone above its point of projection 2. You throw a ball with a speed of 25 ms-1 at 40˚ above the horizontal directly towards a wall. The wall is 22m from the release point of the ball. (a) How long is the ball in the air before it hits the wall? (b) How far above the release point does the ball hit the wall? (c) What are the horizontal and vertical components of its velocity as it hits the wall? (d) Has it passed the highest point on its trajectory? 3. During volcanic eruptions, chunks of solid rock can be blasted out of the volcano; these projectiles are called volcanic blocks (a) What initial speed would a block have to be ejected, at 35˚ to the horizontal from the vent A in order to fall at the foot of the volcano at B? (b) What is the time of flight?

35˚

3.3 km

9.4 km