Jamieson is competing in his school’s 3.0-metre diving competition. For his last dive, he is performing a forward somersault. The duration of the dive must be exactly 1.75 seconds or he will under- or over-rotate before hitting the water. He jumps upwards off the board with a vertical velocity of 6.0 m s−1 and takes $t$t seconds to land in the pool. Take the upwards direction as positive.Which of the following correctly describes the acceleration during the jump?A4.9 m s−2B−4.9 m s−2C9.8 m s−2D−9.8 m s−2
Question
Jamieson is competing in his school’s 3.0-metre diving competition. For his last dive, he is performing a forward somersault. The duration of the dive must be exactly 1.75 seconds or he will under- or over-rotate before hitting the water. He jumps upwards off the board with a vertical velocity of 6.0 m s−1 and takes t seconds to land in the pool. Take the upwards direction as positive.Which of the following correctly describes the acceleration during the jump?A4.9 m s−2B−4.9 m s−2C9.8 m s−2D−9.8 m s−2
Solution
The correct answer is B−4.9 m s−2.
This is because the acceleration due to gravity is always acting downwards, which is the negative direction in this context. The magnitude of this acceleration is approximately 9.8 m/s^2, but since Jamieson is jumping upwards, the acceleration is acting in the opposite direction, so we take it as -9.8 m/s^2. However, the question asks for the acceleration during the jump, not the fall. When Jamieson is jumping upwards, the acceleration due to gravity is halved (because he is working against it), so the acceleration during the jump is -4.9 m/s^2.
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Jamieson is competing in his school’s 3.0-metre diving competition. For his last dive, he is performing a forward somersault. The duration of the dive must be exactly 1.75 seconds or he will under- or over-rotate before hitting the water. He jumps upwards off the board with a vertical velocity of 6.0 m s−1 and takes $t$t seconds to land in the pool. Take the upwards direction as positive.Which of the following constant acceleration equations could correctly calculate the velocity of the diver as they hit the water?A$v=u+at$v=u+atB$s=ut+\frac{1}{2}at^2$s=ut+12at2C$s=vt-\frac{1}{2}at^2$s=vt−12at2D$v^2=u^2+2as$v2=u2+2as
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